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	$234.55	4.698%	$245.5692	$245.57	$245.55	$245.60
Purchase #2	$40.56	10.398%	$44.7774	$44.78	$44.80	$44.80
Purchase #3	$238.88	13.489%	$271.1025	$271.10	$271.10	$271.10
Purchase #4	$67.34	6.510%	$71.7238	$71.72	$71.70	$71.70
Purchase #5	$69.49	5.800%	$73.5204	$73.52	$73.50	$73.50
Purchase #6	$175.77	8.540%	$190.7808	$190.78	$190.80	$190.80
Purchase #7	$191.55	13.769%	$217.9245	$217.92	$217.90	$217.90
7 purchase totals =	$1,018.14		$1,115.3986	$1,115.39	$1,115.35	$1,115.40