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 $162.75   4.175%   $169.5448   $169.54   $169.55   $169.50  
  Purchase #2 $204.99   6.772%   $218.8719   $218.87   $218.85   $218.90  
  Purchase #3 $136.84   5.797%   $144.7726   $144.77   $144.75   $144.80  
  Purchase #4 $43.89   7.649%   $47.2471   $47.25   $47.25   $47.20  
  Purchase #5 $206.77   7.528%   $222.3356   $222.34   $222.35   $222.30  
  Purchase #6 $54.37   6.257%   $57.7719   $57.77   $57.75   $57.80  
  Purchase #7 $89.48   3.323%   $92.4534   $92.45   $92.45   $92.50  
  7 purchase totals = $899.09       $952.9973   $952.99   $952.95   $953.00