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 $55.85   9.746%   $61.2931   $61.29   $61.30   $61.30  
  Purchase #2 $202.98   6.793%   $216.7684   $216.77   $216.75   $216.80  
  Purchase #3 $69.60   11.862%   $77.856   $77.86   $77.85   $77.90  
  Purchase #4 $8.68   13.166%   $9.8228   $9.82   $9.80   $9.80  
  Purchase #5 $157.99   8.166%   $170.8915   $170.89   $170.90   $170.90  
  Purchase #6 $182.28   3.412%   $188.4994   $188.50   $188.50   $188.50  
  Purchase #7 $230.34   13.122%   $260.5652   $260.57   $260.55   $260.60  
  7 purchase totals = $907.72       $985.6964   $985.70   $985.65   $985.80