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 $116.60   13.750%   $132.6325   $132.63   $132.65   $132.60  
  Purchase #2 $48.69   6.272%   $51.7438   $51.74   $51.75   $51.70  
  Purchase #3 $43.57   9.620%   $47.7614   $47.76   $47.75   $47.80  
  Purchase #4 $173.60   5.651%   $183.4101   $183.41   $183.40   $183.40  
  Purchase #5 $239.34   7.487%   $257.2594   $257.26   $257.25   $257.30  
  Purchase #6 $148.72   11.810%   $166.2838   $166.28   $166.30   $166.30  
  Purchase #7 $213.51   8.415%   $231.4769   $231.48   $231.50   $231.50  
  7 purchase totals = $984.03       $1,070.5679   $1,070.56   $1,070.60   $1,070.60