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	$5.75	8.755%	$6.2534	$6.25	$6.25	$6.30
Purchase #2	$163.53	9.349%	$178.8184	$178.82	$178.80	$178.80
Purchase #3	$185.33	5.153%	$194.8801	$194.88	$194.90	$194.90
Purchase #4	$105.61	11.824%	$118.0973	$118.10	$118.10	$118.10
Purchase #5	$55.25	11.780%	$61.7585	$61.76	$61.75	$61.80
Purchase #6	$43.55	5.471%	$45.9326	$45.93	$45.95	$45.90
Purchase #7	$132.52	6.188%	$140.7203	$140.72	$140.70	$140.70
7 purchase totals =	$691.54		$746.4606	$746.46	$746.45	$746.50