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 $162.43   6.871%   $173.5906   $173.59   $173.60   $173.60  
  Purchase #2 $56.45   8.181%   $61.0682   $61.07   $61.05   $61.10  
  Purchase #3 $151.45   5.186%   $159.3042   $159.30   $159.30   $159.30  
  Purchase #4 $83.54   4.485%   $87.2868   $87.29   $87.30   $87.30  
  Purchase #5 $234.55   11.713%   $262.0228   $262.02   $262.00   $262.00  
  Purchase #6 $58.70   5.487%   $61.9209   $61.92   $61.90   $61.90  
  Purchase #7 $218.27   4.260%   $227.5683   $227.57   $227.55   $227.60  
  7 purchase totals = $965.39       $1,032.7618   $1,032.76   $1,032.70   $1,032.80