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	$69.55	11.822%	$77.7722	$77.77	$77.75	$77.80
Purchase #2	$245.27	8.257%	$265.5219	$265.52	$265.50	$265.50
Purchase #3	$210.99	5.815%	$223.2591	$223.26	$223.25	$223.30
Purchase #4	$180.84	5.151%	$190.1551	$190.16	$190.15	$190.20
Purchase #5	$250.78	11.859%	$280.52	$280.52	$280.50	$280.50
Purchase #6	$231.91	9.849%	$254.7508	$254.75	$254.75	$254.80
Purchase #7	$173.91	12.826%	$196.2157	$196.22	$196.20	$196.20
7 purchase totals =	$1,363.25		$1,488.1948	$1,488.20	$1,488.10	$1,488.30