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 $54.50   8.698%   $59.2404   $59.24   $59.25   $59.20  
  Purchase #2 $127.91   6.598%   $136.3495   $136.35   $136.35   $136.30  
  Purchase #3 $188.68   5.649%   $199.3385   $199.34   $199.35   $199.30  
  Purchase #4 $95.95   8.638%   $104.2382   $104.24   $104.25   $104.20  
  Purchase #5 $214.84   6.279%   $228.3298   $228.33   $228.35   $228.30  
  Purchase #6 $240.89   8.803%   $262.0955   $262.10   $262.10   $262.10  
  Purchase #7 $217.78   3.761%   $225.9707   $225.97   $225.95   $226.00  
  7 purchase totals = $1,140.55       $1,215.5626   $1,215.57   $1,215.60   $1,215.40