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	$146.26	6.844%	$156.27	$156.27	$156.25	$156.30
Purchase #2	$212.54	12.163%	$238.3912	$238.39	$238.40	$238.40
Purchase #3	$243.33	13.613%	$276.4545	$276.45	$276.45	$276.50
Purchase #4	$97.73	7.384%	$104.9464	$104.95	$104.95	$104.90
Purchase #5	$63.80	9.154%	$69.6403	$69.64	$69.65	$69.60
Purchase #6	$30.42	7.747%	$32.7766	$32.78	$32.80	$32.80
Purchase #7	$119.51	6.183%	$126.8993	$126.90	$126.90	$126.90
7 purchase totals =	$913.59		$1,005.3783	$1,005.38	$1,005.40	$1,005.40