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 $248.60   7.528%   $267.3146   $267.31   $267.30   $267.30  
  Purchase #2 $54.27   8.648%   $58.9633   $58.96   $58.95   $59.00  
  Purchase #3 $103.90   11.557%   $115.9077   $115.91   $115.90   $115.90  
  Purchase #4 $52.38   3.843%   $54.393   $54.39   $54.40   $54.40  
  Purchase #5 $184.52   7.633%   $198.6044   $198.60   $198.60   $198.60  
  Purchase #6 $63.92   6.632%   $68.1592   $68.16   $68.15   $68.20  
  Purchase #7 $49.77   13.798%   $56.6373   $56.64   $56.65   $56.60  
  7 purchase totals = $757.36       $819.9795   $819.97   $819.95   $820.00