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 $84.65   3.109%   $87.2818   $87.28   $87.30   $87.30  
  Purchase #2 $87.93   4.450%   $91.8429   $91.84   $91.85   $91.80  
  Purchase #3 $209.77   9.364%   $229.4129   $229.41   $229.40   $229.40  
  Purchase #4 $37.64   9.361%   $41.1635   $41.16   $41.15   $41.20  
  Purchase #5 $189.48   6.226%   $201.277   $201.28   $201.30   $201.30  
  Purchase #6 $187.29   13.396%   $212.3794   $212.38   $212.40   $212.40  
  Purchase #7 $84.99   6.663%   $90.6529   $90.65   $90.65   $90.70  
  7 purchase totals = $881.75       $954.0104   $954.00   $954.05   $954.10