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	$13.59	13.402%	$15.4113	$15.41	$15.40	$15.40
Purchase #2	$59.40	13.515%	$67.4279	$67.43	$67.45	$67.40
Purchase #3	$91.48	13.571%	$103.8948	$103.89	$103.90	$103.90
Purchase #4	$45.74	10.344%	$50.4713	$50.47	$50.45	$50.50
Purchase #5	$153.90	12.804%	$173.6054	$173.61	$173.60	$173.60
Purchase #6	$5.85	7.727%	$6.302	$6.30	$6.30	$6.30
Purchase #7	$64.62	11.868%	$72.2891	$72.29	$72.30	$72.30
7 purchase totals =	$434.58		$489.4018	$489.40	$489.40	$489.40