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 $66.47   4.398%   $69.3934   $69.39   $69.40   $69.40  
  Purchase #2 $41.75   11.715%   $46.641   $46.64   $46.65   $46.60  
  Purchase #3 $61.66   13.484%   $69.9742   $69.97   $69.95   $70.00  
  Purchase #4 $246.25   11.479%   $274.517   $274.52   $274.50   $274.50  
  Purchase #5 $25.95   4.335%   $27.0749   $27.07   $27.05   $27.10  
  Purchase #6 $178.73   10.392%   $197.3036   $197.30   $197.30   $197.30  
  Purchase #7 $146.69   13.362%   $166.2907   $166.29   $166.30   $166.30  
  7 purchase totals = $767.50       $851.1948   $851.18   $851.15   $851.20