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 $75.58   10.306%   $83.3693   $83.37   $83.35   $83.40  
  Purchase #2 $119.53   5.848%   $126.5201   $126.52   $126.50   $126.50  
  Purchase #3 $226.44   9.197%   $247.2657   $247.27   $247.25   $247.30  
  Purchase #4 $9.56   12.263%   $10.7323   $10.73   $10.75   $10.70  
  Purchase #5 $168.49   12.728%   $189.9354   $189.94   $189.95   $189.90  
  Purchase #6 $154.52   5.255%   $162.64   $162.64   $162.65   $162.60  
  Purchase #7 $76.60   8.226%   $82.9011   $82.90   $82.90   $82.90  
  7 purchase totals = $830.72       $903.3639   $903.37   $903.35   $903.30