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 $118.92   6.389%   $126.5178   $126.52   $126.50   $126.50  
  Purchase #2 $158.46   9.695%   $173.8227   $173.82   $173.80   $173.80  
  Purchase #3 $8.73   7.291%   $9.3665   $9.37   $9.35   $9.40  
  Purchase #4 $234.92   5.334%   $247.4506   $247.45   $247.45   $247.50  
  Purchase #5 $21.46   4.823%   $22.495   $22.50   $22.50   $22.50  
  Purchase #6 $217.32   7.294%   $233.1713   $233.17   $233.15   $233.20  
  Purchase #7 $145.30   13.439%   $164.8269   $164.83   $164.85   $164.80  
  7 purchase totals = $905.11       $977.6508   $977.66   $977.60   $977.70