Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $105.89   13.190%   $119.8569   $119.86   $119.85   $119.90  
  Purchase #2 $212.25   13.694%   $241.3155   $241.32   $241.30   $241.30  
  Purchase #3 $92.84   11.462%   $103.4813   $103.48   $103.50   $103.50  
  Purchase #4 $209.97   13.458%   $238.2278   $238.23   $238.25   $238.20  
  Purchase #5 $160.93   9.115%   $175.5988   $175.60   $175.60   $175.60  
  Purchase #6 $193.49   5.532%   $204.1939   $204.19   $204.20   $204.20  
  Purchase #7 $199.81   9.732%   $219.2555   $219.26   $219.25   $219.30  
  7 purchase totals = $1,175.18       $1,301.9297   $1,301.94   $1,301.95   $1,302.00