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	$250.25	11.639%	$279.3766	$279.38	$279.40	$279.40
Purchase #2	$36.84	9.124%	$40.2013	$40.20	$40.20	$40.20
Purchase #3	$42.47	6.196%	$45.1014	$45.10	$45.10	$45.10
Purchase #4	$120.91	9.436%	$132.3191	$132.32	$132.30	$132.30
Purchase #5	$236.36	8.588%	$256.6586	$256.66	$256.65	$256.70
Purchase #6	$125.82	7.713%	$135.5245	$135.52	$135.50	$135.50
Purchase #7	$243.98	12.848%	$275.3266	$275.33	$275.35	$275.30
7 purchase totals =	$1,056.63		$1,164.5081	$1,164.51	$1,164.50	$1,164.50