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 $153.63   5.617%   $162.2594   $162.26   $162.25   $162.30  
  Purchase #2 $249.79   6.457%   $265.9189   $265.92   $265.90   $265.90  
  Purchase #3 $85.60   13.669%   $97.3007   $97.30   $97.30   $97.30  
  Purchase #4 $66.97   10.834%   $74.2255   $74.23   $74.25   $74.20  
  Purchase #5 $81.62   10.206%   $89.9501   $89.95   $89.95   $90.00  
  Purchase #6 $172.54   9.409%   $188.7743   $188.77   $188.75   $188.80  
  Purchase #7 $36.59   13.307%   $41.459   $41.46   $41.45   $41.50  
  7 purchase totals = $846.74       $919.8879   $919.89   $919.85   $920.00