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 $106.44   7.146%   $114.0462   $114.05   $114.05   $114.00  
  Purchase #2 $38.93   11.227%   $43.3007   $43.30   $43.30   $43.30  
  Purchase #3 $91.35   5.351%   $96.2381   $96.24   $96.25   $96.20  
  Purchase #4 $243.89   4.664%   $255.265   $255.27   $255.25   $255.30  
  Purchase #5 $17.45   3.298%   $18.0255   $18.03   $18.05   $18.00  
  Purchase #6 $76.88   10.835%   $85.2099   $85.21   $85.20   $85.20  
  Purchase #7 $230.51   10.287%   $254.2226   $254.22   $254.20   $254.20  
  7 purchase totals = $805.45       $866.3080   $866.32   $866.30   $866.20