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	$37.73	12.148%	$42.3134	$42.31	$42.30	$42.30
Purchase #2	$210.69	11.517%	$234.9552	$234.96	$234.95	$235.00
Purchase #3	$42.39	5.304%	$44.6384	$44.64	$44.65	$44.60
Purchase #4	$168.37	4.536%	$176.0073	$176.01	$176.00	$176.00
Purchase #5	$234.45	5.563%	$247.4925	$247.49	$247.50	$247.50
Purchase #6	$226.31	12.452%	$254.4901	$254.49	$254.50	$254.50
Purchase #7	$80.37	11.702%	$89.7749	$89.77	$89.75	$89.80
7 purchase totals =	$1,000.31		$1,089.6718	$1,089.67	$1,089.65	$1,089.70