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 $56.88   5.326%   $59.9094   $59.91   $59.90   $59.90  
  Purchase #2 $238.91   8.113%   $258.2928   $258.29   $258.30   $258.30  
  Purchase #3 $92.45   4.519%   $96.6278   $96.63   $96.65   $96.60  
  Purchase #4 $175.89   9.273%   $192.2003   $192.20   $192.20   $192.20  
  Purchase #5 $233.65   6.703%   $249.3116   $249.31   $249.30   $249.30  
  Purchase #6 $24.53   10.639%   $27.1397   $27.14   $27.15   $27.10  
  Purchase #7 $169.45   6.591%   $180.6184   $180.62   $180.60   $180.60  
  7 purchase totals = $991.76       $1,064.1000   $1,064.10   $1,064.10   $1,064.00