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 $241.25   5.690%   $254.9771   $254.98   $255.00   $255.00  
  Purchase #2 $96.48   8.619%   $104.7956   $104.80   $104.80   $104.80  
  Purchase #3 $129.81   5.761%   $137.2884   $137.29   $137.30   $137.30  
  Purchase #4 $77.43   5.814%   $81.9318   $81.93   $81.95   $81.90  
  Purchase #5 $71.62   4.747%   $75.0198   $75.02   $75.00   $75.00  
  Purchase #6 $121.41   7.730%   $130.795   $130.80   $130.80   $130.80  
  Purchase #7 $220.96   6.788%   $235.9588   $235.96   $235.95   $236.00  
  7 purchase totals = $958.96       $1,020.7665   $1,020.78   $1,020.80   $1,020.80