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 $191.25   6.717%   $204.0963   $204.10   $204.10   $204.10  
  Purchase #2 $136.46   4.382%   $142.4397   $142.44   $142.45   $142.40  
  Purchase #3 $84.78   3.243%   $87.5294   $87.53   $87.55   $87.50  
  Purchase #4 $135.46   4.459%   $141.5002   $141.50   $141.50   $141.50  
  Purchase #5 $246.49   3.836%   $255.9454   $255.95   $255.95   $255.90  
  Purchase #6 $94.86   7.328%   $101.8113   $101.81   $101.80   $101.80  
  Purchase #7 $65.92   7.470%   $70.8442   $70.84   $70.85   $70.80  
  7 purchase totals = $955.22       $1,004.1665   $1,004.17   $1,004.20   $1,004.00