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 $159.48   8.769%   $173.4648   $173.46   $173.45   $173.50  
  Purchase #2 $123.73   7.115%   $132.5334   $132.53   $132.55   $132.50  
  Purchase #3 $43.73   7.245%   $46.8982   $46.90   $46.90   $46.90  
  Purchase #4 $50.61   5.197%   $53.2402   $53.24   $53.25   $53.20  
  Purchase #5 $185.70   11.130%   $206.3684   $206.37   $206.35   $206.40  
  Purchase #6 $50.75   11.637%   $56.6558   $56.66   $56.65   $56.70  
  Purchase #7 $147.67   6.212%   $156.8433   $156.84   $156.85   $156.80  
  7 purchase totals = $761.67       $826.0041   $826.00   $826.00   $826.00