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 $47.64   3.303%   $49.2135   $49.21   $49.20   $49.20  
  Purchase #2 $165.71   12.702%   $186.7585   $186.76   $186.75   $186.80  
  Purchase #3 $180.95   7.848%   $195.151   $195.15   $195.15   $195.20  
  Purchase #4 $82.35   4.676%   $86.2007   $86.20   $86.20   $86.20  
  Purchase #5 $203.98   7.506%   $219.2907   $219.29   $219.30   $219.30  
  Purchase #6 $16.54   12.866%   $18.668   $18.67   $18.65   $18.70  
  Purchase #7 $208.29   4.370%   $217.3923   $217.39   $217.40   $217.40  
  7 purchase totals = $905.46       $972.6747   $972.67   $972.65   $972.80