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 $249.88   4.869%   $262.0467   $262.05   $262.05   $262.00  
  Purchase #2 $226.56   3.659%   $234.8498   $234.85   $234.85   $234.80  
  Purchase #3 $196.68   11.675%   $219.6424   $219.64   $219.65   $219.60  
  Purchase #4 $108.72   9.605%   $119.1626   $119.16   $119.15   $119.20  
  Purchase #5 $27.90   11.639%   $31.1473   $31.15   $31.15   $31.10  
  Purchase #6 $100.75   9.131%   $109.9495   $109.95   $109.95   $109.90  
  Purchase #7 $135.27   6.756%   $144.4088   $144.41   $144.40   $144.40  
  7 purchase totals = $1,045.76       $1,121.2071   $1,121.21   $1,121.20   $1,121.00