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 $196.62   13.206%   $222.5856   $222.59   $222.60   $222.60  
  Purchase #2 $206.99   9.145%   $225.9192   $225.92   $225.90   $225.90  
  Purchase #3 $120.33   5.222%   $126.6136   $126.61   $126.60   $126.60  
  Purchase #4 $173.77   11.686%   $194.0768   $194.08   $194.10   $194.10  
  Purchase #5 $56.28   13.780%   $64.0354   $64.04   $64.05   $64.00  
  Purchase #6 $117.84   12.434%   $132.4922   $132.49   $132.50   $132.50  
  Purchase #7 $33.91   7.706%   $36.5231   $36.52   $36.50   $36.50  
  7 purchase totals = $905.74       $1,002.2459   $1,002.25   $1,002.25   $1,002.20