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 $242.88   12.811%   $273.9954   $274.00   $274.00   $274.00  
  Purchase #2 $42.48   11.413%   $47.3282   $47.33   $47.35   $47.30  
  Purchase #3 $161.66   4.361%   $168.71   $168.71   $168.70   $168.70  
  Purchase #4 $163.49   12.409%   $183.7775   $183.78   $183.80   $183.80  
  Purchase #5 $82.41   7.261%   $88.3938   $88.39   $88.40   $88.40  
  Purchase #6 $145.37   10.192%   $160.1861   $160.19   $160.20   $160.20  
  Purchase #7 $221.80   7.105%   $237.5589   $237.56   $237.55   $237.60  
  7 purchase totals = $1,060.09       $1,159.9499   $1,159.96   $1,160.00   $1,160.00