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 $67.38   13.318%   $76.3537   $76.35   $76.35   $76.40  
  Purchase #2 $30.38   6.772%   $32.4373   $32.44   $32.45   $32.40  
  Purchase #3 $75.27   3.794%   $78.1257   $78.13   $78.15   $78.10  
  Purchase #4 $161.75   8.608%   $175.6734   $175.67   $175.65   $175.70  
  Purchase #5 $165.26   4.368%   $172.4786   $172.48   $172.50   $172.50  
  Purchase #6 $217.92   6.307%   $231.6642   $231.66   $231.65   $231.70  
  Purchase #7 $31.57   10.646%   $34.9309   $34.93   $34.95   $34.90  
  7 purchase totals = $749.53       $801.6638   $801.66   $801.70   $801.70