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 $192.26   8.170%   $207.9676   $207.97   $207.95   $208.00  
  Purchase #2 $97.93   13.703%   $111.3493   $111.35   $111.35   $111.30  
  Purchase #3 $53.37   9.785%   $58.5923   $58.59   $58.60   $58.60  
  Purchase #4 $143.77   10.612%   $159.0269   $159.03   $159.05   $159.00  
  Purchase #5 $235.41   3.355%   $243.308   $243.31   $243.30   $243.30  
  Purchase #6 $163.90   12.621%   $184.5858   $184.59   $184.60   $184.60  
  Purchase #7 $201.25   3.626%   $208.5473   $208.55   $208.55   $208.50  
  7 purchase totals = $1,087.89       $1,173.3772   $1,173.39   $1,173.40   $1,173.30