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 $231.41   5.811%   $244.8572   $244.86   $244.85   $244.90  
  Purchase #2 $166.90   11.232%   $185.6462   $185.65   $185.65   $185.60  
  Purchase #3 $215.46   11.728%   $240.7291   $240.73   $240.75   $240.70  
  Purchase #4 $230.27   3.819%   $239.064   $239.06   $239.05   $239.10  
  Purchase #5 $93.43   9.874%   $102.6553   $102.66   $102.65   $102.70  
  Purchase #6 $162.31   13.803%   $184.7136   $184.71   $184.70   $184.70  
  Purchase #7 $166.40   5.463%   $175.4904   $175.49   $175.50   $175.50  
  7 purchase totals = $1,266.18       $1,373.1558   $1,373.16   $1,373.15   $1,373.20