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 $14.41   4.195%   $15.0145   $15.01   $15.00   $15.00  
  Purchase #2 $195.81   11.797%   $218.9097   $218.91   $218.90   $218.90  
  Purchase #3 $177.98   8.636%   $193.3504   $193.35   $193.35   $193.40  
  Purchase #4 $152.53   6.554%   $162.5268   $162.53   $162.55   $162.50  
  Purchase #5 $58.37   4.577%   $61.0416   $61.04   $61.05   $61.00  
  Purchase #6 $73.50   11.313%   $81.8151   $81.82   $81.80   $81.80  
  Purchase #7 $32.64   5.404%   $34.4039   $34.40   $34.40   $34.40  
  7 purchase totals = $705.24       $767.0620   $767.06   $767.05   $767.00