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 $198.92   6.108%   $211.07   $211.07   $211.05   $211.10  
  Purchase #2 $46.54   13.825%   $52.9742   $52.97   $52.95   $53.00  
  Purchase #3 $158.48   9.203%   $173.0649   $173.06   $173.05   $173.10  
  Purchase #4 $119.67   7.158%   $128.236   $128.24   $128.25   $128.20  
  Purchase #5 $84.45   7.734%   $90.9814   $90.98   $91.00   $91.00  
  Purchase #6 $192.39   8.554%   $208.847   $208.85   $208.85   $208.80  
  Purchase #7 $96.82   4.146%   $100.8342   $100.83   $100.85   $100.80  
  7 purchase totals = $897.27       $966.0077   $966.00   $966.00   $966.00