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 $86.99   13.279%   $98.5414   $98.54   $98.55   $98.50  
  Purchase #2 $81.69   8.197%   $88.3861   $88.39   $88.40   $88.40  
  Purchase #3 $90.47   13.858%   $103.0073   $103.01   $103.00   $103.00  
  Purchase #4 $65.49   4.237%   $68.2648   $68.26   $68.25   $68.30  
  Purchase #5 $177.41   11.630%   $198.0428   $198.04   $198.05   $198.00  
  Purchase #6 $248.50   11.272%   $276.5109   $276.51   $276.50   $276.50  
  Purchase #7 $121.33   12.268%   $136.2148   $136.21   $136.20   $136.20  
  7 purchase totals = $871.88       $968.9681   $968.96   $968.95   $968.90