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 $89.59   7.759%   $96.5413   $96.54   $96.55   $96.50  
  Purchase #2 $50.56   12.616%   $56.9386   $56.94   $56.95   $56.90  
  Purchase #3 $106.54   3.819%   $110.6088   $110.61   $110.60   $110.60  
  Purchase #4 $24.70   6.501%   $26.3057   $26.31   $26.30   $26.30  
  Purchase #5 $172.49   5.744%   $182.3978   $182.40   $182.40   $182.40  
  Purchase #6 $201.41   12.318%   $226.2197   $226.22   $226.20   $226.20  
  Purchase #7 $92.65   3.112%   $95.5333   $95.53   $95.55   $95.50  
  7 purchase totals = $737.94       $794.5452   $794.55   $794.55   $794.40