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 $208.29   12.449%   $234.22   $234.22   $234.20   $234.20  
  Purchase #2 $108.93   9.192%   $118.9428   $118.94   $118.95   $118.90  
  Purchase #3 $80.64   7.261%   $86.4953   $86.50   $86.50   $86.50  
  Purchase #4 $109.28   11.580%   $121.9346   $121.93   $121.95   $121.90  
  Purchase #5 $60.74   4.393%   $63.4083   $63.41   $63.40   $63.40  
  Purchase #6 $238.33   6.293%   $253.3281   $253.33   $253.35   $253.30  
  Purchase #7 $248.80   12.554%   $280.0344   $280.03   $280.05   $280.00  
  7 purchase totals = $1,055.01       $1,158.3635   $1,158.36   $1,158.40   $1,158.20