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 $91.58   4.733%   $95.9145   $95.91   $95.90   $95.90  
  Purchase #2 $86.25   5.854%   $91.2991   $91.30   $91.30   $91.30  
  Purchase #3 $48.92   13.546%   $55.5467   $55.55   $55.55   $55.50  
  Purchase #4 $35.29   10.755%   $39.0854   $39.09   $39.10   $39.10  
  Purchase #5 $123.69   9.515%   $135.4591   $135.46   $135.45   $135.50  
  Purchase #6 $157.63   7.102%   $168.8249   $168.82   $168.80   $168.80  
  Purchase #7 $207.94   6.375%   $221.1962   $221.20   $221.20   $221.20  
  7 purchase totals = $751.30       $807.3259   $807.33   $807.30   $807.30