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 $200.41   3.812%   $208.0496   $208.05   $208.05   $208.00  
  Purchase #2 $68.46   3.130%   $70.6028   $70.60   $70.60   $70.60  
  Purchase #3 $63.42   4.644%   $66.3652   $66.37   $66.35   $66.40  
  Purchase #4 $225.38   5.404%   $237.5595   $237.56   $237.55   $237.60  
  Purchase #5 $155.63   8.446%   $168.7745   $168.77   $168.75   $168.80  
  Purchase #6 $11.68   9.167%   $12.7507   $12.75   $12.75   $12.80  
  Purchase #7 $216.98   8.823%   $236.1241   $236.12   $236.10   $236.10  
  7 purchase totals = $941.96       $1,000.2264   $1,000.22   $1,000.15   $1,000.30