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	$206.61	7.718%	$222.5562	$222.56	$222.55	$222.60
Purchase #2	$81.51	11.701%	$91.0475	$91.05	$91.05	$91.00
Purchase #3	$244.72	12.627%	$275.6208	$275.62	$275.60	$275.60
Purchase #4	$165.45	11.303%	$184.1508	$184.15	$184.15	$184.20
Purchase #5	$171.64	10.665%	$189.9454	$189.95	$189.95	$189.90
Purchase #6	$153.90	8.264%	$166.6183	$166.62	$166.60	$166.60
Purchase #7	$52.38	6.375%	$55.7192	$55.72	$55.70	$55.70
7 purchase totals =	$1,076.21		$1,185.6582	$1,185.67	$1,185.60	$1,185.60