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 $164.54   10.796%   $182.3037   $182.30   $182.30   $182.30  
  Purchase #2 $239.62   5.655%   $253.1705   $253.17   $253.15   $253.20  
  Purchase #3 $170.45   11.137%   $189.433   $189.43   $189.45   $189.40  
  Purchase #4 $119.27   6.143%   $126.5968   $126.60   $126.60   $126.60  
  Purchase #5 $114.92   5.843%   $121.6348   $121.63   $121.65   $121.60  
  Purchase #6 $219.89   7.123%   $235.5528   $235.55   $235.55   $235.60  
  Purchase #7 $39.99   5.809%   $42.313   $42.31   $42.30   $42.30  
  7 purchase totals = $1,068.68       $1,151.0046   $1,150.99   $1,151.00   $1,151.00