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 $196.90   11.183%   $218.9193   $218.92   $218.90   $218.90  
  Purchase #2 $209.36   13.644%   $237.9251   $237.93   $237.95   $237.90  
  Purchase #3 $116.43   8.858%   $126.7434   $126.74   $126.75   $126.70  
  Purchase #4 $203.34   11.177%   $226.0673   $226.07   $226.05   $226.10  
  Purchase #5 $165.48   10.735%   $183.2443   $183.24   $183.25   $183.20  
  Purchase #6 $103.42   9.748%   $113.5014   $113.50   $113.50   $113.50  
  Purchase #7 $49.34   7.636%   $53.1076   $53.11   $53.10   $53.10  
  7 purchase totals = $1,044.27       $1,159.5084   $1,159.51   $1,159.50   $1,159.40