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 $123.80   4.500%   $129.371   $129.37   $129.35   $129.40  
  Purchase #2 $147.60   4.146%   $153.7195   $153.72   $153.70   $153.70  
  Purchase #3 $100.86   8.233%   $109.1638   $109.16   $109.15   $109.20  
  Purchase #4 $115.30   7.252%   $123.6616   $123.66   $123.65   $123.70  
  Purchase #5 $31.89   5.242%   $33.5617   $33.56   $33.55   $33.60  
  Purchase #6 $71.53   11.424%   $79.7016   $79.70   $79.70   $79.70  
  Purchase #7 $119.70   10.793%   $132.6192   $132.62   $132.60   $132.60  
  7 purchase totals = $710.68       $761.7984   $761.79   $761.70   $761.90