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 $166.43   10.683%   $184.2097   $184.21   $184.20   $184.20  
  Purchase #2 $145.92   11.387%   $162.5359   $162.54   $162.55   $162.50  
  Purchase #3 $93.47   11.746%   $104.449   $104.45   $104.45   $104.40  
  Purchase #4 $215.76   8.752%   $234.6433   $234.64   $234.65   $234.60  
  Purchase #5 $37.52   10.870%   $41.5984   $41.60   $41.60   $41.60  
  Purchase #6 $65.85   4.588%   $68.8712   $68.87   $68.85   $68.90  
  Purchase #7 $53.32   10.567%   $58.9543   $58.95   $58.95   $59.00  
  7 purchase totals = $778.27       $855.2618   $855.26   $855.25   $855.20