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 $161.56   12.661%   $182.0151   $182.02   $182.00   $182.00  
  Purchase #2 $167.94   4.566%   $175.6081   $175.61   $175.60   $175.60  
  Purchase #3 $158.78   4.727%   $166.2855   $166.29   $166.30   $166.30  
  Purchase #4 $142.34   3.765%   $147.6991   $147.70   $147.70   $147.70  
  Purchase #5 $59.99   6.484%   $63.8798   $63.88   $63.90   $63.90  
  Purchase #6 $124.71   6.619%   $132.9646   $132.96   $132.95   $133.00  
  Purchase #7 $11.50   6.726%   $12.2735   $12.27   $12.25   $12.30  
  7 purchase totals = $826.82       $880.7257   $880.73   $880.70   $880.80