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 $52.85   5.814%   $55.9227   $55.92   $55.90   $55.90  
  Purchase #2 $125.87   8.553%   $136.6357   $136.64   $136.65   $136.60  
  Purchase #3 $60.47   3.702%   $62.7086   $62.71   $62.70   $62.70  
  Purchase #4 $177.26   6.766%   $189.2534   $189.25   $189.25   $189.30  
  Purchase #5 $67.90   5.757%   $71.809   $71.81   $71.80   $71.80  
  Purchase #6 $224.60   10.322%   $247.7832   $247.78   $247.80   $247.80  
  Purchase #7 $83.42   4.374%   $87.0688   $87.07   $87.05   $87.10  
  7 purchase totals = $792.37       $851.1814   $851.18   $851.15   $851.20