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 $104.31   13.365%   $118.251   $118.25   $118.25   $118.30  
  Purchase #2 $11.42   6.511%   $12.1636   $12.16   $12.15   $12.20  
  Purchase #3 $125.90   3.240%   $129.9792   $129.98   $130.00   $130.00  
  Purchase #4 $82.94   4.784%   $86.9078   $86.91   $86.90   $86.90  
  Purchase #5 $221.83   9.423%   $242.733   $242.73   $242.75   $242.70  
  Purchase #6 $134.78   12.763%   $151.982   $151.98   $152.00   $152.00  
  Purchase #7 $237.53   9.344%   $259.7248   $259.72   $259.70   $259.70  
  7 purchase totals = $918.71       $1,001.7414   $1,001.73   $1,001.75   $1,001.80