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 $161.32   4.708%   $168.9149   $168.91   $168.90   $168.90  
  Purchase #2 $224.79   8.248%   $243.3307   $243.33   $243.35   $243.30  
  Purchase #3 $49.64   10.775%   $54.9887   $54.99   $55.00   $55.00  
  Purchase #4 $233.56   13.773%   $265.7282   $265.73   $265.75   $265.70  
  Purchase #5 $220.54   8.263%   $238.7632   $238.76   $238.75   $238.80  
  Purchase #6 $199.51   11.624%   $222.701   $222.70   $222.70   $222.70  
  Purchase #7 $60.48   12.478%   $68.0267   $68.03   $68.05   $68.00  
  7 purchase totals = $1,149.84       $1,262.4534   $1,262.45   $1,262.50   $1,262.40