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 $41.76   13.178%   $47.2631   $47.26   $47.25   $47.30  
  Purchase #2 $95.91   6.658%   $102.2957   $102.30   $102.30   $102.30  
  Purchase #3 $179.44   5.761%   $189.7775   $189.78   $189.80   $189.80  
  Purchase #4 $229.26   8.258%   $248.1923   $248.19   $248.20   $248.20  
  Purchase #5 $132.94   12.307%   $149.3009   $149.30   $149.30   $149.30  
  Purchase #6 $30.90   8.798%   $33.6186   $33.62   $33.60   $33.60  
  Purchase #7 $137.67   5.573%   $145.3423   $145.34   $145.35   $145.30  
  7 purchase totals = $847.88       $915.7904   $915.79   $915.80   $915.80