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 $71.98   12.503%   $80.9797   $80.98   $81.00   $81.00  
  Purchase #2 $132.73   4.869%   $139.1926   $139.19   $139.20   $139.20  
  Purchase #3 $58.93   13.516%   $66.895   $66.90   $66.90   $66.90  
  Purchase #4 $147.49   13.175%   $166.9218   $166.92   $166.90   $166.90  
  Purchase #5 $80.44   13.696%   $91.4571   $91.46   $91.45   $91.50  
  Purchase #6 $166.77   9.149%   $182.0278   $182.03   $182.05   $182.00  
  Purchase #7 $121.98   10.496%   $134.783   $134.78   $134.80   $134.80  
  7 purchase totals = $780.32       $862.2570   $862.26   $862.30   $862.30