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 $31.92   3.762%   $33.1208   $33.12   $33.10   $33.10  
  Purchase #2 $192.96   9.537%   $211.3626   $211.36   $211.35   $211.40  
  Purchase #3 $161.26   8.757%   $175.3815   $175.38   $175.40   $175.40  
  Purchase #4 $144.81   5.685%   $153.0424   $153.04   $153.05   $153.00  
  Purchase #5 $39.81   11.749%   $44.4873   $44.49   $44.50   $44.50  
  Purchase #6 $210.75   5.556%   $222.4593   $222.46   $222.45   $222.50  
  Purchase #7 $10.84   13.441%   $12.297   $12.30   $12.30   $12.30  
  7 purchase totals = $792.35       $852.1509   $852.15   $852.15   $852.20