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 $36.99   12.408%   $41.5797   $41.58   $41.60   $41.60  
  Purchase #2 $117.45   11.533%   $130.9955   $131.00   $131.00   $131.00  
  Purchase #3 $141.87   3.159%   $146.3517   $146.35   $146.35   $146.40  
  Purchase #4 $19.58   10.250%   $21.587   $21.59   $21.60   $21.60  
  Purchase #5 $72.88   3.678%   $75.5605   $75.56   $75.55   $75.60  
  Purchase #6 $166.29   3.300%   $171.7776   $171.78   $171.80   $171.80  
  Purchase #7 $179.32   8.379%   $194.3452   $194.35   $194.35   $194.30  
  7 purchase totals = $734.38       $782.1972   $782.21   $782.25   $782.30