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	$131.88	11.868%	$147.5315	$147.53	$147.55	$147.50
Purchase #2	$116.63	9.599%	$127.8253	$127.83	$127.85	$127.80
Purchase #3	$245.69	8.701%	$267.0675	$267.07	$267.05	$267.10
Purchase #4	$189.47	12.188%	$212.5626	$212.56	$212.55	$212.60
Purchase #5	$235.40	8.521%	$255.4584	$255.46	$255.45	$255.50
Purchase #6	$224.47	9.659%	$246.1516	$246.15	$246.15	$246.20
Purchase #7	$67.36	6.196%	$71.5336	$71.53	$71.55	$71.50
7 purchase totals =	$1,210.90		$1,328.1305	$1,328.13	$1,328.15	$1,328.20