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 $70.63   5.142%   $74.2618   $74.26   $74.25   $74.30  
  Purchase #2 $107.69   10.701%   $119.2139   $119.21   $119.20   $119.20  
  Purchase #3 $70.40   3.351%   $72.7591   $72.76   $72.75   $72.80  
  Purchase #4 $99.91   3.553%   $103.4598   $103.46   $103.45   $103.50  
  Purchase #5 $33.94   12.872%   $38.3088   $38.31   $38.30   $38.30  
  Purchase #6 $110.44   10.452%   $121.9832   $121.98   $122.00   $122.00  
  Purchase #7 $215.31   10.424%   $237.7539   $237.75   $237.75   $237.80  
  7 purchase totals = $708.32       $767.7405   $767.73   $767.70   $767.90