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 $241.41   10.562%   $266.9077   $266.91   $266.90   $266.90  
  Purchase #2 $123.55   7.168%   $132.4061   $132.41   $132.40   $132.40  
  Purchase #3 $156.42   7.673%   $168.4221   $168.42   $168.40   $168.40  
  Purchase #4 $116.57   8.282%   $126.2243   $126.22   $126.20   $126.20  
  Purchase #5 $74.39   9.346%   $81.3425   $81.34   $81.35   $81.30  
  Purchase #6 $243.51   5.267%   $256.3357   $256.34   $256.35   $256.30  
  Purchase #7 $211.88   3.460%   $219.211   $219.21   $219.20   $219.20  
  7 purchase totals = $1,167.73       $1,250.8494   $1,250.85   $1,250.80   $1,250.70