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 $223.56   12.548%   $251.6123   $251.61   $251.60   $251.60  
  Purchase #2 $202.53   7.473%   $217.6651   $217.67   $217.65   $217.70  
  Purchase #3 $61.85   11.504%   $68.9652   $68.97   $68.95   $69.00  
  Purchase #4 $48.79   4.438%   $50.9553   $50.96   $50.95   $51.00  
  Purchase #5 $60.39   13.565%   $68.5819   $68.58   $68.60   $68.60  
  Purchase #6 $23.72   8.425%   $25.7184   $25.72   $25.70   $25.70  
  Purchase #7 $240.95   10.803%   $266.9798   $266.98   $267.00   $267.00  
  7 purchase totals = $861.79       $950.4780   $950.49   $950.45   $950.60