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 $14.85   11.689%   $16.5858   $16.59   $16.60   $16.60  
  Purchase #2 $203.57   5.393%   $214.5485   $214.55   $214.55   $214.50  
  Purchase #3 $10.69   12.369%   $12.0122   $12.01   $12.00   $12.00  
  Purchase #4 $245.84   9.553%   $269.3251   $269.33   $269.35   $269.30  
  Purchase #5 $141.37   12.665%   $159.2745   $159.27   $159.25   $159.30  
  Purchase #6 $86.50   10.419%   $95.5124   $95.51   $95.50   $95.50  
  Purchase #7 $46.84   5.448%   $49.3918   $49.39   $49.40   $49.40  
  7 purchase totals = $749.66       $816.6503   $816.65   $816.65   $816.60