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 $78.77   10.233%   $86.8305   $86.83   $86.85   $86.80  
  Purchase #2 $153.69   7.831%   $165.7255   $165.73   $165.75   $165.70  
  Purchase #3 $195.43   5.618%   $206.4093   $206.41   $206.40   $206.40  
  Purchase #4 $151.91   7.828%   $163.8015   $163.80   $163.80   $163.80  
  Purchase #5 $196.93   10.288%   $217.1902   $217.19   $217.20   $217.20  
  Purchase #6 $45.54   4.607%   $47.638   $47.64   $47.65   $47.60  
  Purchase #7 $209.60   8.455%   $227.3217   $227.32   $227.30   $227.30  
  7 purchase totals = $1,031.87       $1,114.9167   $1,114.92   $1,114.95   $1,114.80