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 $97.29   12.674%   $109.6205   $109.62   $109.60   $109.60  
  Purchase #2 $61.68   3.198%   $63.6525   $63.65   $63.65   $63.70  
  Purchase #3 $72.86   7.530%   $78.3464   $78.35   $78.35   $78.30  
  Purchase #4 $15.50   8.762%   $16.8581   $16.86   $16.85   $16.90  
  Purchase #5 $86.59   11.709%   $96.7288   $96.73   $96.75   $96.70  
  Purchase #6 $205.90   3.397%   $212.8944   $212.89   $212.90   $212.90  
  Purchase #7 $195.31   4.764%   $204.6146   $204.61   $204.60   $204.60  
  7 purchase totals = $735.13       $782.7153   $782.71   $782.70   $782.70