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 $103.64   3.311%   $107.0715   $107.07   $107.05   $107.10  
  Purchase #2 $208.26   10.465%   $230.0544   $230.05   $230.05   $230.10  
  Purchase #3 $76.59   8.173%   $82.8497   $82.85   $82.85   $82.80  
  Purchase #4 $188.57   4.813%   $197.6459   $197.65   $197.65   $197.60  
  Purchase #5 $76.67   12.169%   $86   $86.00   $86.00   $86.00  
  Purchase #6 $96.77   7.532%   $104.0587   $104.06   $104.05   $104.10  
  Purchase #7 $131.76   10.306%   $145.3392   $145.34   $145.35   $145.30  
  7 purchase totals = $882.26       $953.0194   $953.02   $953.00   $953.00