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 $192.44   7.399%   $206.6786   $206.68   $206.70   $206.70  
  Purchase #2 $67.89   12.444%   $76.3382   $76.34   $76.35   $76.30  
  Purchase #3 $27.66   9.522%   $30.2938   $30.29   $30.30   $30.30  
  Purchase #4 $200.75   6.555%   $213.9092   $213.91   $213.90   $213.90  
  Purchase #5 $246.50   10.130%   $271.4705   $271.47   $271.45   $271.50  
  Purchase #6 $24.59   11.630%   $27.4498   $27.45   $27.45   $27.40  
  Purchase #7 $66.46   10.366%   $73.3492   $73.35   $73.35   $73.30  
  7 purchase totals = $826.29       $899.4893   $899.49   $899.50   $899.40