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 $86.59   6.757%   $92.4409   $92.44   $92.45   $92.40  
  Purchase #2 $202.96   10.676%   $224.628   $224.63   $224.65   $224.60  
  Purchase #3 $180.69   3.257%   $186.5751   $186.58   $186.60   $186.60  
  Purchase #4 $221.68   11.209%   $246.5281   $246.53   $246.55   $246.50  
  Purchase #5 $5.86   9.842%   $6.4367   $6.44   $6.45   $6.40  
  Purchase #6 $217.43   4.347%   $226.8817   $226.88   $226.90   $226.90  
  Purchase #7 $245.59   11.116%   $272.8898   $272.89   $272.90   $272.90  
  7 purchase totals = $1,160.80       $1,256.3803   $1,256.39   $1,256.50   $1,256.30