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 $233.95   5.727%   $247.3483   $247.35   $247.35   $247.30  
  Purchase #2 $137.55   6.359%   $146.2968   $146.30   $146.30   $146.30  
  Purchase #3 $157.37   12.265%   $176.6714   $176.67   $176.65   $176.70  
  Purchase #4 $8.89   7.235%   $9.5332   $9.53   $9.55   $9.50  
  Purchase #5 $69.61   8.517%   $75.5387   $75.54   $75.55   $75.50  
  Purchase #6 $154.80   11.715%   $172.9348   $172.93   $172.95   $172.90  
  Purchase #7 $138.85   5.721%   $146.7936   $146.79   $146.80   $146.80  
  7 purchase totals = $901.02       $975.1168   $975.11   $975.15   $975.00