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 $237.74   3.599%   $246.2963   $246.30   $246.30   $246.30  
  Purchase #2 $21.32   5.791%   $22.5546   $22.55   $22.55   $22.60  
  Purchase #3 $116.65   10.741%   $129.1794   $129.18   $129.20   $129.20  
  Purchase #4 $216.42   3.788%   $224.618   $224.62   $224.60   $224.60  
  Purchase #5 $175.63   11.493%   $195.8152   $195.82   $195.80   $195.80  
  Purchase #6 $166.79   11.453%   $185.8925   $185.89   $185.90   $185.90  
  Purchase #7 $192.73   5.282%   $202.91   $202.91   $202.90   $202.90  
  7 purchase totals = $1,127.28       $1,207.2660   $1,207.27   $1,207.25   $1,207.30