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 $246.44   9.154%   $268.9991   $269.00   $269.00   $269.00  
  Purchase #2 $15.90   12.670%   $17.9145   $17.91   $17.90   $17.90  
  Purchase #3 $141.92   9.456%   $155.34   $155.34   $155.35   $155.30  
  Purchase #4 $73.94   6.473%   $78.7261   $78.73   $78.75   $78.70  
  Purchase #5 $242.93   4.462%   $253.7695   $253.77   $253.75   $253.80  
  Purchase #6 $16.90   5.484%   $17.8268   $17.83   $17.85   $17.80  
  Purchase #7 $216.85   12.747%   $244.4919   $244.49   $244.50   $244.50  
  7 purchase totals = $954.88       $1,037.0679   $1,037.07   $1,037.10   $1,037.00