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 $88.61   11.221%   $98.5529   $98.55   $98.55   $98.60  
  Purchase #2 $61.40   11.677%   $68.5697   $68.57   $68.55   $68.60  
  Purchase #3 $236.83   13.239%   $268.1839   $268.18   $268.20   $268.20  
  Purchase #4 $167.63   9.191%   $183.0369   $183.04   $183.05   $183.00  
  Purchase #5 $232.32   4.300%   $242.3098   $242.31   $242.30   $242.30  
  Purchase #6 $238.39   13.339%   $270.1888   $270.19   $270.20   $270.20  
  Purchase #7 $176.46   12.281%   $198.1311   $198.13   $198.15   $198.10  
  7 purchase totals = $1,201.64       $1,328.9731   $1,328.97   $1,329.00   $1,329.00