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 $200.53   6.220%   $213.003   $213.00   $213.00   $213.00  
  Purchase #2 $144.68   3.302%   $149.4573   $149.46   $149.45   $149.50  
  Purchase #3 $133.55   9.551%   $146.3054   $146.31   $146.30   $146.30  
  Purchase #4 $129.86   12.708%   $146.3626   $146.36   $146.35   $146.40  
  Purchase #5 $232.70   12.446%   $261.6618   $261.66   $261.65   $261.70  
  Purchase #6 $58.34   6.699%   $62.2482   $62.25   $62.25   $62.20  
  Purchase #7 $43.36   8.403%   $47.0035   $47.00   $47.00   $47.00  
  7 purchase totals = $943.02       $1,026.0418   $1,026.04   $1,026.00   $1,026.10