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 $213.35   12.292%   $239.575   $239.58   $239.60   $239.60  
  Purchase #2 $186.31   5.710%   $196.9483   $196.95   $196.95   $196.90  
  Purchase #3 $22.89   7.225%   $24.5438   $24.54   $24.55   $24.50  
  Purchase #4 $141.79   3.815%   $147.1993   $147.20   $147.20   $147.20  
  Purchase #5 $140.45   13.654%   $159.627   $159.63   $159.65   $159.60  
  Purchase #6 $48.82   6.177%   $51.8356   $51.84   $51.85   $51.80  
  Purchase #7 $208.29   8.364%   $225.7114   $225.71   $225.70   $225.70  
  7 purchase totals = $961.90       $1,045.4404   $1,045.45   $1,045.50   $1,045.30