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	$51.52	6.770%	$55.0079	$55.01	$55.00	$55.00
Purchase #2	$65.92	9.303%	$72.0525	$72.05	$72.05	$72.10
Purchase #3	$179.82	5.327%	$189.399	$189.40	$189.40	$189.40
Purchase #4	$233.41	13.677%	$265.3335	$265.33	$265.35	$265.30
Purchase #5	$134.31	6.636%	$143.2228	$143.22	$143.20	$143.20
Purchase #6	$247.49	13.292%	$280.3864	$280.39	$280.40	$280.40
Purchase #7	$140.39	13.197%	$158.9173	$158.92	$158.90	$158.90
7 purchase totals =	$1,052.86		$1,164.3194	$1,164.32	$1,164.30	$1,164.30