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 $211.90   11.564%   $236.4041   $236.40   $236.40   $236.40  
  Purchase #2 $5.30   10.543%   $5.8588   $5.86   $5.85   $5.90  
  Purchase #3 $157.70   13.357%   $178.764   $178.76   $178.75   $178.80  
  Purchase #4 $72.78   7.294%   $78.0886   $78.09   $78.10   $78.10  
  Purchase #5 $222.26   8.677%   $241.5455   $241.55   $241.55   $241.50  
  Purchase #6 $60.82   5.181%   $63.9711   $63.97   $63.95   $64.00  
  Purchase #7 $233.64   10.570%   $258.3357   $258.34   $258.35   $258.30  
  7 purchase totals = $964.40       $1,062.9678   $1,062.97   $1,062.95   $1,063.00