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 $239.81   10.743%   $265.5728   $265.57   $265.55   $265.60  
  Purchase #2 $183.87   12.220%   $206.3389   $206.34   $206.35   $206.30  
  Purchase #3 $78.26   12.714%   $88.21   $88.21   $88.20   $88.20  
  Purchase #4 $167.51   5.757%   $177.1536   $177.15   $177.15   $177.20  
  Purchase #5 $249.58   4.299%   $260.3094   $260.31   $260.30   $260.30  
  Purchase #6 $116.59   4.148%   $121.4262   $121.43   $121.45   $121.40  
  Purchase #7 $30.39   11.584%   $33.9104   $33.91   $33.90   $33.90  
  7 purchase totals = $1,066.01       $1,152.9213   $1,152.92   $1,152.90   $1,152.90