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 $247.71   10.453%   $273.6031   $273.60   $273.60   $273.60  
  Purchase #2 $191.30   6.619%   $203.9621   $203.96   $203.95   $204.00  
  Purchase #3 $63.46   10.703%   $70.2521   $70.25   $70.25   $70.30  
  Purchase #4 $222.63   7.533%   $239.4007   $239.40   $239.40   $239.40  
  Purchase #5 $219.73   6.585%   $234.1992   $234.20   $234.20   $234.20  
  Purchase #6 $205.37   9.670%   $225.2293   $225.23   $225.25   $225.20  
  Purchase #7 $100.37   5.285%   $105.6746   $105.67   $105.65   $105.70  
  7 purchase totals = $1,250.57       $1,352.3211   $1,352.31   $1,352.30   $1,352.40