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 $214.35   5.745%   $226.6644   $226.66   $226.65   $226.70  
  Purchase #2 $119.39   5.816%   $126.3337   $126.33   $126.35   $126.30  
  Purchase #3 $171.95   3.628%   $178.1883   $178.19   $178.20   $178.20  
  Purchase #4 $110.60   13.488%   $125.5177   $125.52   $125.50   $125.50  
  Purchase #5 $114.38   5.815%   $121.0312   $121.03   $121.05   $121.00  
  Purchase #6 $146.74   10.339%   $161.9114   $161.91   $161.90   $161.90  
  Purchase #7 $40.49   12.407%   $45.5136   $45.51   $45.50   $45.50  
  7 purchase totals = $917.90       $985.1603   $985.15   $985.15   $985.10