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 $61.92   9.539%   $67.8265   $67.83   $67.85   $67.80  
  Purchase #2 $224.43   9.669%   $246.1301   $246.13   $246.15   $246.10  
  Purchase #3 $85.79   9.247%   $93.723   $93.72   $93.70   $93.70  
  Purchase #4 $144.86   12.385%   $162.8009   $162.80   $162.80   $162.80  
  Purchase #5 $168.52   8.517%   $182.8728   $182.87   $182.85   $182.90  
  Purchase #6 $71.54   10.471%   $79.031   $79.03   $79.05   $79.00  
  Purchase #7 $12.26   12.498%   $13.7923   $13.79   $13.80   $13.80  
  7 purchase totals = $769.32       $846.1766   $846.17   $846.20   $846.10