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	$183.73	3.863%	$190.8275	$190.83	$190.85	$190.80
Purchase #2	$189.74	5.416%	$200.0163	$200.02	$200.00	$200.00
Purchase #3	$104.77	6.635%	$111.7215	$111.72	$111.70	$111.70
Purchase #4	$25.59	8.783%	$27.8376	$27.84	$27.85	$27.80
Purchase #5	$88.29	12.361%	$99.2035	$99.20	$99.20	$99.20
Purchase #6	$41.47	3.698%	$43.0036	$43.00	$43.00	$43.00
Purchase #7	$136.91	12.412%	$153.9033	$153.90	$153.90	$153.90
7 purchase totals =	$770.50		$826.5133	$826.51	$826.50	$826.40