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 $26.43   12.193%   $29.6526   $29.65   $29.65   $29.70  
  Purchase #2 $240.84   10.548%   $266.2438   $266.24   $266.25   $266.20  
  Purchase #3 $57.76   12.272%   $64.8483   $64.85   $64.85   $64.80  
  Purchase #4 $57.58   12.692%   $64.8881   $64.89   $64.90   $64.90  
  Purchase #5 $163.33   9.392%   $178.67   $178.67   $178.65   $178.70  
  Purchase #6 $11.64   10.403%   $12.8509   $12.85   $12.85   $12.90  
  Purchase #7 $55.66   4.823%   $58.3445   $58.34   $58.35   $58.30  
  7 purchase totals = $613.24       $675.4982   $675.49   $675.50   $675.50