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	$235.57	8.674%	$256.0033	$256.00	$256.00	$256.00
Purchase #2	$47.31	5.500%	$49.9121	$49.91	$49.90	$49.90
Purchase #3	$120.72	5.583%	$127.4598	$127.46	$127.45	$127.50
Purchase #4	$20.90	8.281%	$22.6307	$22.63	$22.65	$22.60
Purchase #5	$123.61	11.502%	$137.8276	$137.83	$137.85	$137.80
Purchase #6	$49.50	7.802%	$53.362	$53.36	$53.35	$53.40
Purchase #7	$75.64	12.515%	$85.1063	$85.11	$85.10	$85.10
7 purchase totals =	$673.25		$732.3018	$732.30	$732.30	$732.30