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 $82.63   5.371%   $87.0681   $87.07   $87.05   $87.10  
  Purchase #2 $91.62   8.811%   $99.6926   $99.69   $99.70   $99.70  
  Purchase #3 $121.70   13.629%   $138.2865   $138.29   $138.30   $138.30  
  Purchase #4 $89.29   5.780%   $94.451   $94.45   $94.45   $94.50  
  Purchase #5 $42.71   3.484%   $44.198   $44.20   $44.20   $44.20  
  Purchase #6 $59.39   5.564%   $62.6945   $62.69   $62.70   $62.70  
  Purchase #7 $208.54   8.621%   $226.5182   $226.52   $226.50   $226.50  
  7 purchase totals = $695.88       $752.9089   $752.91   $752.90   $753.00