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	$122.42	4.131%	$127.4772	$127.48	$127.50	$127.50
Purchase #2	$136.74	10.253%	$150.76	$150.76	$150.75	$150.80
Purchase #3	$145.25	6.271%	$154.3586	$154.36	$154.35	$154.40
Purchase #4	$174.27	8.862%	$189.7138	$189.71	$189.70	$189.70
Purchase #5	$191.46	8.660%	$208.0404	$208.04	$208.05	$208.00
Purchase #6	$200.92	7.572%	$216.1337	$216.13	$216.15	$216.10
Purchase #7	$240.90	8.630%	$261.6897	$261.69	$261.70	$261.70
7 purchase totals =	$1,211.96		$1,308.1734	$1,308.17	$1,308.20	$1,308.20