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 $33.65   10.761%   $37.2711   $37.27   $37.25   $37.30  
  Purchase #2 $151.85   9.468%   $166.2272   $166.23   $166.25   $166.20  
  Purchase #3 $36.84   10.234%   $40.6102   $40.61   $40.60   $40.60  
  Purchase #4 $129.84   6.626%   $138.4432   $138.44   $138.45   $138.40  
  Purchase #5 $175.49   7.674%   $188.9571   $188.96   $188.95   $189.00  
  Purchase #6 $216.92   9.613%   $237.7725   $237.77   $237.75   $237.80  
  Purchase #7 $246.66   3.177%   $254.4964   $254.50   $254.50   $254.50  
  7 purchase totals = $991.25       $1,063.7777   $1,063.78   $1,063.75   $1,063.80