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 $191.92   8.868%   $208.9395   $208.94   $208.95   $208.90  
  Purchase #2 $211.50   9.519%   $231.6327   $231.63   $231.65   $231.60  
  Purchase #3 $170.77   9.130%   $186.3613   $186.36   $186.35   $186.40  
  Purchase #4 $71.69   7.867%   $77.3299   $77.33   $77.35   $77.30  
  Purchase #5 $245.55   8.325%   $265.992   $265.99   $266.00   $266.00  
  Purchase #6 $42.86   9.866%   $47.0886   $47.09   $47.10   $47.10  
  Purchase #7 $27.91   12.407%   $31.3728   $31.37   $31.35   $31.40  
  7 purchase totals = $962.20       $1,048.7168   $1,048.71   $1,048.75   $1,048.70