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	$129.39	7.816%	$139.5031	$139.50	$139.50	$139.50
Purchase #2	$125.83	11.227%	$139.9569	$139.96	$139.95	$140.00
Purchase #3	$245.90	9.659%	$269.6515	$269.65	$269.65	$269.70
Purchase #4	$72.54	5.338%	$76.4122	$76.41	$76.40	$76.40
Purchase #5	$187.91	4.441%	$196.2551	$196.26	$196.25	$196.30
Purchase #6	$13.27	11.798%	$14.8356	$14.84	$14.85	$14.80
Purchase #7	$148.90	12.402%	$167.3666	$167.37	$167.35	$167.40
7 purchase totals =	$923.74		$1,003.9810	$1,003.99	$1,003.95	$1,004.10