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	$120.95	11.825%	$135.2523	$135.25	$135.25	$135.30
Purchase #2	$189.43	5.433%	$199.7217	$199.72	$199.70	$199.70
Purchase #3	$31.27	4.457%	$32.6637	$32.66	$32.65	$32.70
Purchase #4	$40.42	7.385%	$43.405	$43.41	$43.40	$43.40
Purchase #5	$67.31	4.331%	$70.2252	$70.23	$70.25	$70.20
Purchase #6	$67.31	7.572%	$72.4067	$72.41	$72.40	$72.40
Purchase #7	$206.43	7.766%	$222.4614	$222.46	$222.45	$222.50
7 purchase totals =	$723.12		$776.1360	$776.14	$776.10	$776.20