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 $236.83   13.602%   $269.0436   $269.04   $269.05   $269.00  
  Purchase #2 $95.68   8.262%   $103.5851   $103.59   $103.60   $103.60  
  Purchase #3 $45.59   12.610%   $51.3389   $51.34   $51.35   $51.30  
  Purchase #4 $214.59   7.266%   $230.1821   $230.18   $230.20   $230.20  
  Purchase #5 $98.45   3.136%   $101.5374   $101.54   $101.55   $101.50  
  Purchase #6 $186.83   9.385%   $204.364   $204.36   $204.35   $204.40  
  Purchase #7 $89.89   9.346%   $98.2911   $98.29   $98.30   $98.30  
  7 purchase totals = $967.86       $1,058.3422   $1,058.34   $1,058.40   $1,058.30