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	$28.50	13.718%	$32.4096	$32.41	$32.40	$32.40
Purchase #2	$9.64	9.724%	$10.5774	$10.58	$10.60	$10.60
Purchase #3	$26.62	9.785%	$29.2248	$29.22	$29.20	$29.20
Purchase #4	$175.25	7.578%	$188.5304	$188.53	$188.55	$188.50
Purchase #5	$88.59	12.677%	$99.8206	$99.82	$99.80	$99.80
Purchase #6	$80.26	4.398%	$83.7898	$83.79	$83.80	$83.80
Purchase #7	$45.52	4.319%	$47.486	$47.49	$47.50	$47.50
7 purchase totals =	$454.38		$491.8386	$491.84	$491.85	$491.80