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 $110.71   7.124%   $118.597   $118.60   $118.60   $118.60  
  Purchase #2 $86.82   11.380%   $96.7001   $96.70   $96.70   $96.70  
  Purchase #3 $68.37   4.776%   $71.6354   $71.64   $71.65   $71.60  
  Purchase #4 $241.64   8.262%   $261.6043   $261.60   $261.60   $261.60  
  Purchase #5 $234.26   6.463%   $249.4002   $249.40   $249.40   $249.40  
  Purchase #6 $127.73   3.687%   $132.4394   $132.44   $132.45   $132.40  
  Purchase #7 $58.50   9.600%   $64.116   $64.12   $64.10   $64.10  
  7 purchase totals = $928.03       $994.4924   $994.50   $994.50   $994.40