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	$50.64	3.695%	$52.5111	$52.51	$52.50	$52.50
Purchase #2	$42.97	5.680%	$45.4107	$45.41	$45.40	$45.40
Purchase #3	$131.34	12.253%	$147.4331	$147.43	$147.45	$147.40
Purchase #4	$211.64	7.692%	$227.9193	$227.92	$227.90	$227.90
Purchase #5	$173.57	9.731%	$190.4601	$190.46	$190.45	$190.50
Purchase #6	$233.56	5.805%	$247.1182	$247.12	$247.10	$247.10
Purchase #7	$202.43	13.184%	$229.1184	$229.12	$229.10	$229.10
7 purchase totals =	$1,046.15		$1,139.9709	$1,139.97	$1,139.90	$1,139.90