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	$120.72	6.580%	$128.6634	$128.66	$128.65	$128.70
Purchase #2	$247.39	7.483%	$265.9022	$265.90	$265.90	$265.90
Purchase #3	$86.63	11.754%	$96.8125	$96.81	$96.80	$96.80
Purchase #4	$65.89	9.176%	$71.9361	$71.94	$71.95	$71.90
Purchase #5	$156.63	10.624%	$173.2704	$173.27	$173.25	$173.30
Purchase #6	$174.74	3.300%	$180.5064	$180.51	$180.50	$180.50
Purchase #7	$187.76	12.776%	$211.7482	$211.75	$211.75	$211.70
7 purchase totals =	$1,039.76		$1,128.8392	$1,128.84	$1,128.80	$1,128.80