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 $104.63   10.183%   $115.2845   $115.28   $115.30   $115.30  
  Purchase #2 $23.93   11.657%   $26.7195   $26.72   $26.70   $26.70  
  Purchase #3 $165.31   4.367%   $172.5291   $172.53   $172.55   $172.50  
  Purchase #4 $82.91   9.551%   $90.8287   $90.83   $90.85   $90.80  
  Purchase #5 $126.71   13.293%   $143.5536   $143.55   $143.55   $143.60  
  Purchase #6 $60.73   10.522%   $67.12   $67.12   $67.10   $67.10  
  Purchase #7 $132.75   8.506%   $144.0417   $144.04   $144.05   $144.00  
  7 purchase totals = $696.97       $760.0771   $760.07   $760.10   $760.00