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 $54.95   4.827%   $57.6024   $57.60   $57.60   $57.60  
  Purchase #2 $27.80   6.530%   $29.6153   $29.62   $29.60   $29.60  
  Purchase #3 $53.66   11.242%   $59.6925   $59.69   $59.70   $59.70  
  Purchase #4 $219.40   3.282%   $226.6007   $226.60   $226.60   $226.60  
  Purchase #5 $171.58   12.676%   $193.3295   $193.33   $193.35   $193.30  
  Purchase #6 $68.42   9.679%   $75.0424   $75.04   $75.05   $75.00  
  Purchase #7 $139.88   13.469%   $158.7204   $158.72   $158.70   $158.70  
  7 purchase totals = $735.69       $800.6032   $800.60   $800.60   $800.50