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 $87.46   9.694%   $95.9384   $95.94   $95.95   $95.90  
  Purchase #2 $241.80   9.669%   $265.1796   $265.18   $265.20   $265.20  
  Purchase #3 $152.47   3.461%   $157.747   $157.75   $157.75   $157.70  
  Purchase #4 $204.65   12.482%   $230.1944   $230.19   $230.20   $230.20  
  Purchase #5 $226.98   12.461%   $255.264   $255.26   $255.25   $255.30  
  Purchase #6 $62.31   13.370%   $70.6408   $70.64   $70.65   $70.60  
  Purchase #7 $219.79   10.805%   $243.5383   $243.54   $243.55   $243.50  
  7 purchase totals = $1,195.46       $1,318.5025   $1,318.50   $1,318.55   $1,318.40