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 $232.42   12.404%   $261.2494   $261.25   $261.25   $261.20  
  Purchase #2 $97.55   9.565%   $106.8807   $106.88   $106.90   $106.90  
  Purchase #3 $248.62   12.415%   $279.4862   $279.49   $279.50   $279.50  
  Purchase #4 $167.83   8.324%   $181.8002   $181.80   $181.80   $181.80  
  Purchase #5 $19.29   6.495%   $20.5429   $20.54   $20.55   $20.50  
  Purchase #6 $37.83   7.184%   $40.5477   $40.55   $40.55   $40.50  
  Purchase #7 $58.60   5.828%   $62.0152   $62.02   $62.00   $62.00  
  7 purchase totals = $862.14       $952.5223   $952.53   $952.55   $952.40