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 $116.51   4.673%   $121.9545   $121.95   $121.95   $122.00  
  Purchase #2 $171.33   7.659%   $184.4522   $184.45   $184.45   $184.50  
  Purchase #3 $226.84   5.860%   $240.1328   $240.13   $240.15   $240.10  
  Purchase #4 $26.46   5.325%   $27.869   $27.87   $27.85   $27.90  
  Purchase #5 $125.27   8.836%   $136.3389   $136.34   $136.35   $136.30  
  Purchase #6 $125.73   5.398%   $132.5169   $132.52   $132.50   $132.50  
  Purchase #7 $28.93   5.261%   $30.452   $30.45   $30.45   $30.50  
  7 purchase totals = $821.07       $873.7163   $873.71   $873.70   $873.80