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 $52.31   7.675%   $56.3248   $56.32   $56.30   $56.30  
  Purchase #2 $234.98   3.772%   $243.8434   $243.84   $243.85   $243.80  
  Purchase #3 $85.56   12.387%   $96.1583   $96.16   $96.15   $96.20  
  Purchase #4 $44.74   8.644%   $48.6073   $48.61   $48.60   $48.60  
  Purchase #5 $122.92   8.300%   $133.1224   $133.12   $133.10   $133.10  
  Purchase #6 $124.33   6.483%   $132.3903   $132.39   $132.40   $132.40  
  Purchase #7 $192.36   7.483%   $206.7543   $206.75   $206.75   $206.80  
  7 purchase totals = $857.20       $917.2008   $917.19   $917.15   $917.20