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 $248.48   5.765%   $262.8049   $262.80   $262.80   $262.80  
  Purchase #2 $231.78   10.599%   $256.3464   $256.35   $256.35   $256.30  
  Purchase #3 $194.73   6.172%   $206.7487   $206.75   $206.75   $206.70  
  Purchase #4 $153.55   4.566%   $160.5611   $160.56   $160.55   $160.60  
  Purchase #5 $42.29   5.819%   $44.7509   $44.75   $44.75   $44.80  
  Purchase #6 $176.69   5.408%   $186.2454   $186.25   $186.25   $186.20  
  Purchase #7 $197.82   9.392%   $216.3993   $216.40   $216.40   $216.40  
  7 purchase totals = $1,245.34       $1,333.8567   $1,333.86   $1,333.85   $1,333.80