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 $53.46   9.747%   $58.6707   $58.67   $58.65   $58.70  
  Purchase #2 $169.65   3.342%   $175.3197   $175.32   $175.30   $175.30  
  Purchase #3 $23.36   4.637%   $24.4432   $24.44   $24.45   $24.40  
  Purchase #4 $115.25   12.254%   $129.3727   $129.37   $129.35   $129.40  
  Purchase #5 $98.65   12.837%   $111.3137   $111.31   $111.30   $111.30  
  Purchase #6 $62.54   10.768%   $69.2743   $69.27   $69.25   $69.30  
  Purchase #7 $179.47   3.585%   $185.904   $185.90   $185.90   $185.90  
  7 purchase totals = $702.38       $754.2983   $754.28   $754.20   $754.30