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	$88.82	6.473%	$94.5693	$94.57	$94.55	$94.60
Purchase #2	$195.77	11.652%	$218.5811	$218.58	$218.60	$218.60
Purchase #3	$47.29	4.633%	$49.4809	$49.48	$49.50	$49.50
Purchase #4	$234.96	10.303%	$259.1679	$259.17	$259.15	$259.20
Purchase #5	$68.47	4.254%	$71.3827	$71.38	$71.40	$71.40
Purchase #6	$56.27	5.763%	$59.5128	$59.51	$59.50	$59.50
Purchase #7	$59.33	10.775%	$65.7228	$65.72	$65.70	$65.70
7 purchase totals =	$750.91		$818.4175	$818.41	$818.40	$818.50