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 $160.66   13.290%   $182.0117   $182.01   $182.00   $182.00  
  Purchase #2 $118.53   5.348%   $124.869   $124.87   $124.85   $124.90  
  Purchase #3 $143.62   6.671%   $153.2009   $153.20   $153.20   $153.20  
  Purchase #4 $170.70   12.513%   $192.0597   $192.06   $192.05   $192.10  
  Purchase #5 $41.73   10.259%   $46.0111   $46.01   $46.00   $46.00  
  Purchase #6 $112.68   6.291%   $119.7687   $119.77   $119.75   $119.80  
  Purchase #7 $8.48   3.468%   $8.7741   $8.77   $8.75   $8.80  
  7 purchase totals = $756.40       $826.6952   $826.69   $826.60   $826.80