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 $241.65   13.521%   $274.3235   $274.32   $274.30   $274.30  
  Purchase #2 $138.82   7.690%   $149.4953   $149.50   $149.50   $149.50  
  Purchase #3 $216.47   3.198%   $223.3927   $223.39   $223.40   $223.40  
  Purchase #4 $125.62   11.612%   $140.207   $140.21   $140.20   $140.20  
  Purchase #5 $63.75   6.430%   $67.8491   $67.85   $67.85   $67.80  
  Purchase #6 $238.85   10.318%   $263.4945   $263.49   $263.50   $263.50  
  Purchase #7 $61.80   4.536%   $64.6032   $64.60   $64.60   $64.60  
  7 purchase totals = $1,086.96       $1,183.3653   $1,183.36   $1,183.35   $1,183.30