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	$120.42	9.124%	$131.4071	$131.41	$131.40	$131.40
Purchase #2	$43.84	13.701%	$49.8465	$49.85	$49.85	$49.80
Purchase #3	$51.59	4.579%	$53.9523	$53.95	$53.95	$54.00
Purchase #4	$110.61	10.758%	$122.5094	$122.51	$122.50	$122.50
Purchase #5	$80.51	6.154%	$85.4646	$85.46	$85.45	$85.50
Purchase #6	$26.31	13.454%	$29.8497	$29.85	$29.85	$29.80
Purchase #7	$25.78	11.129%	$28.6491	$28.65	$28.65	$28.60
7 purchase totals =	$459.06		$501.6787	$501.68	$501.65	$501.60