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	$151.32	13.516%	$171.7724	$171.77	$171.75	$171.80
Purchase #2	$65.69	12.112%	$73.6464	$73.65	$73.65	$73.60
Purchase #3	$71.90	9.368%	$78.6356	$78.64	$78.65	$78.60
Purchase #4	$123.98	10.112%	$136.5169	$136.52	$136.50	$136.50
Purchase #5	$250.69	11.447%	$279.3865	$279.39	$279.40	$279.40
Purchase #6	$65.85	6.361%	$70.0387	$70.04	$70.05	$70.00
Purchase #7	$72.82	7.382%	$78.1956	$78.20	$78.20	$78.20
7 purchase totals =	$802.25		$888.1921	$888.21	$888.20	$888.10