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	$221.56	9.285%	$242.1318	$242.13	$242.15	$242.10
Purchase #2	$33.68	7.804%	$36.3084	$36.31	$36.30	$36.30
Purchase #3	$109.63	13.522%	$124.4542	$124.45	$124.45	$124.50
Purchase #4	$139.41	11.138%	$154.9375	$154.94	$154.95	$154.90
Purchase #5	$58.27	6.195%	$61.8798	$61.88	$61.90	$61.90
Purchase #6	$38.38	9.809%	$42.1447	$42.14	$42.15	$42.10
Purchase #7	$247.74	9.762%	$271.9244	$271.92	$271.90	$271.90
7 purchase totals =	$848.67		$933.7808	$933.77	$933.80	$933.70