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	$111.27	6.281%	$118.2589	$118.26	$118.25	$118.30
Purchase #2	$140.37	4.226%	$146.302	$146.30	$146.30	$146.30
Purchase #3	$55.64	12.399%	$62.5388	$62.54	$62.55	$62.50
Purchase #4	$99.29	11.203%	$110.4135	$110.41	$110.40	$110.40
Purchase #5	$60.42	4.187%	$62.9498	$62.95	$62.95	$62.90
Purchase #6	$193.83	11.718%	$216.543	$216.54	$216.55	$216.50
Purchase #7	$46.45	13.637%	$52.7844	$52.78	$52.80	$52.80
7 purchase totals =	$707.27		$769.7904	$769.78	$769.80	$769.70