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 $72.42   12.202%   $81.2567   $81.26   $81.25   $81.30  
  Purchase #2 $95.52   6.559%   $101.7852   $101.79   $101.80   $101.80  
  Purchase #3 $64.66   10.497%   $71.4474   $71.45   $71.45   $71.40  
  Purchase #4 $203.27   8.164%   $219.865   $219.87   $219.85   $219.90  
  Purchase #5 $113.88   4.311%   $118.7894   $118.79   $118.80   $118.80  
  Purchase #6 $151.48   9.229%   $165.4601   $165.46   $165.45   $165.50  
  Purchase #7 $218.81   3.429%   $226.313   $226.31   $226.30   $226.30  
  7 purchase totals = $920.04       $984.9168   $984.93   $984.90   $985.00