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 $15.80   4.234%   $16.469   $16.47   $16.45   $16.50  
  Purchase #2 $189.54   8.794%   $206.2081   $206.21   $206.20   $206.20  
  Purchase #3 $200.56   8.599%   $217.8062   $217.81   $217.80   $217.80  
  Purchase #4 $126.75   5.250%   $133.4044   $133.40   $133.40   $133.40  
  Purchase #5 $116.31   6.412%   $123.7678   $123.77   $123.75   $123.80  
  Purchase #6 $14.60   10.358%   $16.1123   $16.11   $16.10   $16.10  
  Purchase #7 $156.51   6.405%   $166.5345   $166.53   $166.55   $166.50  
  7 purchase totals = $820.07       $880.3023   $880.30   $880.25   $880.30