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 $134.66   6.581%   $143.522   $143.52   $143.50   $143.50  
  Purchase #2 $168.35   3.199%   $173.7355   $173.74   $173.75   $173.70  
  Purchase #3 $58.87   7.380%   $63.2146   $63.21   $63.20   $63.20  
  Purchase #4 $94.90   4.656%   $99.3185   $99.32   $99.30   $99.30  
  Purchase #5 $207.71   6.838%   $221.9132   $221.91   $221.90   $221.90  
  Purchase #6 $163.37   12.863%   $184.3843   $184.38   $184.40   $184.40  
  Purchase #7 $113.53   10.344%   $125.2735   $125.27   $125.25   $125.30  
  7 purchase totals = $941.39       $1,011.3616   $1,011.35   $1,011.30   $1,011.30