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	$21.52	13.599%	$24.4465	$24.45	$24.45	$24.40
Purchase #2	$6.33	10.112%	$6.9701	$6.97	$6.95	$7.00
Purchase #3	$66.88	6.174%	$71.0092	$71.01	$71.00	$71.00
Purchase #4	$131.47	4.500%	$137.3862	$137.39	$137.40	$137.40
Purchase #5	$130.34	7.111%	$139.6085	$139.61	$139.60	$139.60
Purchase #6	$199.47	5.559%	$210.5585	$210.56	$210.55	$210.60
Purchase #7	$220.88	10.558%	$244.2005	$244.20	$244.20	$244.20
7 purchase totals =	$776.89		$834.1795	$834.19	$834.15	$834.20