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 $248.69   8.159%   $268.9806   $268.98   $269.00   $269.00  
  Purchase #2 $184.71   11.763%   $206.4374   $206.44   $206.45   $206.40  
  Purchase #3 $225.90   5.349%   $237.9834   $237.98   $238.00   $238.00  
  Purchase #4 $211.74   4.552%   $221.3784   $221.38   $221.40   $221.40  
  Purchase #5 $48.80   9.478%   $53.4253   $53.43   $53.45   $53.40  
  Purchase #6 $104.30   6.248%   $110.8167   $110.82   $110.80   $110.80  
  Purchase #7 $75.50   12.503%   $84.9398   $84.94   $84.95   $84.90  
  7 purchase totals = $1,099.64       $1,183.9616   $1,183.97   $1,184.05   $1,183.90