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 $139.68   8.756%   $151.9104   $151.91   $151.90   $151.90  
  Purchase #2 $111.73   13.319%   $126.6113   $126.61   $126.60   $126.60  
  Purchase #3 $165.96   9.677%   $182.0199   $182.02   $182.00   $182.00  
  Purchase #4 $110.85   7.717%   $119.4043   $119.40   $119.40   $119.40  
  Purchase #5 $177.80   3.348%   $183.7527   $183.75   $183.75   $183.80  
  Purchase #6 $118.28   7.114%   $126.6944   $126.69   $126.70   $126.70  
  Purchase #7 $132.28   8.486%   $143.5053   $143.51   $143.50   $143.50  
  7 purchase totals = $956.58       $1,033.8983   $1,033.89   $1,033.85   $1,033.90