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 $194.76   6.182%   $206.8001   $206.80   $206.80   $206.80  
  Purchase #2 $39.95   4.494%   $41.7454   $41.75   $41.75   $41.70  
  Purchase #3 $31.29   12.695%   $35.2623   $35.26   $35.25   $35.30  
  Purchase #4 $109.26   3.772%   $113.3813   $113.38   $113.40   $113.40  
  Purchase #5 $69.41   9.124%   $75.743   $75.74   $75.75   $75.70  
  Purchase #6 $167.79   13.545%   $190.5172   $190.52   $190.50   $190.50  
  Purchase #7 $141.80   3.103%   $146.2001   $146.20   $146.20   $146.20  
  7 purchase totals = $754.26       $809.6494   $809.65   $809.65   $809.60