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 $73.71   8.236%   $79.7808   $79.78   $79.80   $79.80  
  Purchase #2 $151.95   9.872%   $166.9505   $166.95   $166.95   $167.00  
  Purchase #3 $9.88   6.387%   $10.511   $10.51   $10.50   $10.50  
  Purchase #4 $118.95   11.246%   $132.3271   $132.33   $132.35   $132.30  
  Purchase #5 $63.61   3.333%   $65.7301   $65.73   $65.75   $65.70  
  Purchase #6 $154.43   11.525%   $172.2281   $172.23   $172.25   $172.20  
  Purchase #7 $208.83   8.249%   $226.0564   $226.06   $226.05   $226.10  
  7 purchase totals = $781.36       $853.5840   $853.59   $853.65   $853.60