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 $230.75   8.343%   $250.0015   $250.00   $250.00   $250.00  
  Purchase #2 $214.57   13.276%   $243.0563   $243.06   $243.05   $243.10  
  Purchase #3 $173.56   11.789%   $194.021   $194.02   $194.00   $194.00  
  Purchase #4 $111.58   4.259%   $116.3322   $116.33   $116.35   $116.30  
  Purchase #5 $44.63   5.271%   $46.9824   $46.98   $47.00   $47.00  
  Purchase #6 $30.33   9.150%   $33.1052   $33.11   $33.10   $33.10  
  Purchase #7 $214.61   5.401%   $226.2011   $226.20   $226.20   $226.20  
  7 purchase totals = $1,020.03       $1,109.6997   $1,109.70   $1,109.70   $1,109.70