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 $53.50   11.831%   $59.8296   $59.83   $59.85   $59.80  
  Purchase #2 $14.87   7.609%   $16.0015   $16.00   $16.00   $16.00  
  Purchase #3 $157.55   4.203%   $164.1718   $164.17   $164.15   $164.20  
  Purchase #4 $225.54   7.562%   $242.5953   $242.60   $242.60   $242.60  
  Purchase #5 $113.33   4.304%   $118.2077   $118.21   $118.20   $118.20  
  Purchase #6 $149.34   10.406%   $164.8803   $164.88   $164.90   $164.90  
  Purchase #7 $171.27   6.809%   $182.9318   $182.93   $182.95   $182.90  
  7 purchase totals = $885.40       $948.6180   $948.62   $948.65   $948.60