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 $245.27   4.683%   $256.756   $256.76   $256.75   $256.80  
  Purchase #2 $26.57   13.203%   $30.078   $30.08   $30.10   $30.10  
  Purchase #3 $139.80   7.718%   $150.5898   $150.59   $150.60   $150.60  
  Purchase #4 $31.62   12.366%   $35.5301   $35.53   $35.55   $35.50  
  Purchase #5 $131.71   9.351%   $144.0262   $144.03   $144.05   $144.00  
  Purchase #6 $58.85   11.715%   $65.7443   $65.74   $65.75   $65.70  
  Purchase #7 $125.99   12.523%   $141.7677   $141.77   $141.75   $141.80  
  7 purchase totals = $759.81       $824.4921   $824.50   $824.55   $824.50