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 $168.25   7.839%   $181.4391   $181.44   $181.45   $181.40  
  Purchase #2 $193.26   10.228%   $213.0266   $213.03   $213.05   $213.00  
  Purchase #3 $201.26   5.718%   $212.768   $212.77   $212.75   $212.80  
  Purchase #4 $88.52   4.546%   $92.5441   $92.54   $92.55   $92.50  
  Purchase #5 $85.50   3.152%   $88.195   $88.20   $88.20   $88.20  
  Purchase #6 $132.58   5.538%   $139.9223   $139.92   $139.90   $139.90  
  Purchase #7 $66.44   11.725%   $74.2301   $74.23   $74.25   $74.20  
  7 purchase totals = $935.81       $1,002.1252   $1,002.13   $1,002.15   $1,002.00