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	$174.70	12.500%	$196.5375	$196.54	$196.55	$196.50
Purchase #2	$94.59	8.581%	$102.7068	$102.71	$102.70	$102.70
Purchase #3	$89.75	11.548%	$100.1143	$100.11	$100.10	$100.10
Purchase #4	$56.73	13.413%	$64.3392	$64.34	$64.35	$64.30
Purchase #5	$245.44	8.798%	$267.0338	$267.03	$267.05	$267.00
Purchase #6	$63.46	4.188%	$66.1177	$66.12	$66.10	$66.10
Purchase #7	$244.84	10.211%	$269.8406	$269.84	$269.85	$269.80
7 purchase totals =	$969.51		$1,066.6899	$1,066.69	$1,066.70	$1,066.50