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	$46.91	12.818%	$52.9229	$52.92	$52.90	$52.90
Purchase #2	$87.72	13.720%	$99.7552	$99.76	$99.75	$99.80
Purchase #3	$94.40	4.162%	$98.3289	$98.33	$98.35	$98.30
Purchase #4	$241.87	11.399%	$269.4408	$269.44	$269.45	$269.40
Purchase #5	$97.27	8.425%	$105.465	$105.47	$105.45	$105.50
Purchase #6	$24.56	3.388%	$25.3921	$25.39	$25.40	$25.40
Purchase #7	$30.36	9.179%	$33.1467	$33.15	$33.15	$33.10
7 purchase totals =	$623.09		$684.4516	$684.46	$684.45	$684.40