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 $23.65   9.218%   $25.8301   $25.83   $25.85   $25.80  
  Purchase #2 $122.67   11.655%   $136.9672   $136.97   $136.95   $137.00  
  Purchase #3 $244.46   4.780%   $256.1452   $256.15   $256.15   $256.10  
  Purchase #4 $178.98   3.235%   $184.77   $184.77   $184.75   $184.80  
  Purchase #5 $133.90   8.110%   $144.7593   $144.76   $144.75   $144.80  
  Purchase #6 $210.90   12.206%   $236.6425   $236.64   $236.65   $236.60  
  Purchase #7 $27.25   5.821%   $28.8362   $28.84   $28.85   $28.80  
  7 purchase totals = $941.81       $1,013.9505   $1,013.96   $1,013.95   $1,013.90