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 $238.41   9.369%   $260.7466   $260.75   $260.75   $260.70  
  Purchase #2 $90.51   4.502%   $94.5848   $94.58   $94.60   $94.60  
  Purchase #3 $214.62   7.827%   $231.4183   $231.42   $231.40   $231.40  
  Purchase #4 $171.49   3.192%   $176.964   $176.96   $176.95   $177.00  
  Purchase #5 $212.37   13.716%   $241.4987   $241.50   $241.50   $241.50  
  Purchase #6 $104.40   11.617%   $116.5281   $116.53   $116.55   $116.50  
  Purchase #7 $150.81   13.390%   $171.0035   $171.00   $171.00   $171.00  
  7 purchase totals = $1,182.61       $1,292.7440   $1,292.74   $1,292.75   $1,292.70