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 $217.61   13.304%   $246.5608   $246.56   $246.55   $246.60  
  Purchase #2 $44.46   13.573%   $50.4946   $50.49   $50.50   $50.50  
  Purchase #3 $232.68   13.751%   $264.6758   $264.68   $264.70   $264.70  
  Purchase #4 $228.35   9.259%   $249.4929   $249.49   $249.50   $249.50  
  Purchase #5 $191.67   6.566%   $204.2551   $204.26   $204.25   $204.30  
  Purchase #6 $97.36   11.203%   $108.2672   $108.27   $108.25   $108.30  
  Purchase #7 $150.54   10.167%   $165.8454   $165.85   $165.85   $165.80  
  7 purchase totals = $1,162.67       $1,289.5918   $1,289.60   $1,289.60   $1,289.70