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 $116.89   6.305%   $124.2599   $124.26   $124.25   $124.30  
  Purchase #2 $62.98   5.146%   $66.221   $66.22   $66.20   $66.20  
  Purchase #3 $173.68   11.554%   $193.747   $193.75   $193.75   $193.70  
  Purchase #4 $123.34   5.553%   $130.1891   $130.19   $130.20   $130.20  
  Purchase #5 $70.48   12.854%   $79.5395   $79.54   $79.55   $79.50  
  Purchase #6 $218.39   3.636%   $226.3307   $226.33   $226.35   $226.30  
  Purchase #7 $173.50   5.717%   $183.419   $183.42   $183.40   $183.40  
  7 purchase totals = $939.26       $1,003.7062   $1,003.71   $1,003.70   $1,003.60