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 $32.26   3.522%   $33.3962   $33.40   $33.40   $33.40  
  Purchase #2 $153.73   10.174%   $169.3705   $169.37   $169.35   $169.40  
  Purchase #3 $171.35   3.143%   $176.7355   $176.74   $176.75   $176.70  
  Purchase #4 $51.26   10.114%   $56.4444   $56.44   $56.45   $56.40  
  Purchase #5 $209.87   8.667%   $228.0594   $228.06   $228.05   $228.10  
  Purchase #6 $145.82   6.112%   $154.7325   $154.73   $154.75   $154.70  
  Purchase #7 $21.46   4.540%   $22.4343   $22.43   $22.45   $22.40  
  7 purchase totals = $785.75       $841.1728   $841.17   $841.20   $841.10