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 $210.29   7.462%   $225.9818   $225.98   $226.00   $226.00  
  Purchase #2 $231.71   4.378%   $241.8543   $241.85   $241.85   $241.90  
  Purchase #3 $247.63   4.846%   $259.6301   $259.63   $259.65   $259.60  
  Purchase #4 $218.97   8.618%   $237.8408   $237.84   $237.85   $237.80  
  Purchase #5 $219.57   9.750%   $240.9781   $240.98   $241.00   $241.00  
  Purchase #6 $243.53   8.193%   $263.4824   $263.48   $263.50   $263.50  
  Purchase #7 $93.30   8.872%   $101.5776   $101.58   $101.60   $101.60  
  7 purchase totals = $1,465.00       $1,571.3451   $1,571.34   $1,571.45   $1,571.40