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 $113.76   8.865%   $123.8448   $123.84   $123.85   $123.80  
  Purchase #2 $48.55   11.128%   $53.9526   $53.95   $53.95   $54.00  
  Purchase #3 $201.44   12.475%   $226.5696   $226.57   $226.55   $226.60  
  Purchase #4 $114.36   9.323%   $125.0218   $125.02   $125.00   $125.00  
  Purchase #5 $14.60   10.326%   $16.1076   $16.11   $16.10   $16.10  
  Purchase #6 $243.97   9.438%   $266.9959   $267.00   $267.00   $267.00  
  Purchase #7 $180.66   11.378%   $201.2155   $201.22   $201.20   $201.20  
  7 purchase totals = $917.34       $1,013.7078   $1,013.71   $1,013.65   $1,013.70