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 $60.49   10.692%   $66.9576   $66.96   $66.95   $67.00  
  Purchase #2 $147.31   11.688%   $164.5276   $164.53   $164.55   $164.50  
  Purchase #3 $239.58   5.318%   $252.3209   $252.32   $252.30   $252.30  
  Purchase #4 $39.94   9.530%   $43.7463   $43.75   $43.75   $43.70  
  Purchase #5 $59.90   6.441%   $63.7582   $63.76   $63.75   $63.80  
  Purchase #6 $12.49   7.676%   $13.4487   $13.45   $13.45   $13.40  
  Purchase #7 $158.44   3.163%   $163.4515   $163.45   $163.45   $163.50  
  7 purchase totals = $718.15       $768.2108   $768.22   $768.20   $768.20