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	$70.44	11.481%	$78.5272	$78.53	$78.55	$78.50
Purchase #2	$52.25	10.124%	$57.5398	$57.54	$57.55	$57.50
Purchase #3	$170.46	5.414%	$179.6887	$179.69	$179.70	$179.70
Purchase #4	$129.52	12.866%	$146.184	$146.18	$146.20	$146.20
Purchase #5	$134.40	10.158%	$148.0524	$148.05	$148.05	$148.10
Purchase #6	$219.69	6.127%	$233.1504	$233.15	$233.15	$233.20
Purchase #7	$55.48	11.312%	$61.7559	$61.76	$61.75	$61.80
7 purchase totals =	$832.24		$904.8984	$904.90	$904.95	$905.00