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 $116.86   9.242%   $127.6602   $127.66   $127.65   $127.70  
  Purchase #2 $229.99   7.672%   $247.6348   $247.63   $247.65   $247.60  
  Purchase #3 $109.76   10.336%   $121.1048   $121.10   $121.10   $121.10  
  Purchase #4 $218.80   13.121%   $247.5087   $247.51   $247.50   $247.50  
  Purchase #5 $130.43   12.657%   $146.9385   $146.94   $146.95   $146.90  
  Purchase #6 $79.86   3.791%   $82.8875   $82.89   $82.90   $82.90  
  Purchase #7 $222.98   6.281%   $236.9854   $236.99   $237.00   $237.00  
  7 purchase totals = $1,108.68       $1,210.7199   $1,210.72   $1,210.75   $1,210.70