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	$47.28	6.743%	$50.4681	$50.47	$50.45	$50.50
Purchase #2	$91.86	11.729%	$102.6343	$102.63	$102.65	$102.60
Purchase #3	$50.34	12.615%	$56.6904	$56.69	$56.70	$56.70
Purchase #4	$196.90	6.729%	$210.1494	$210.15	$210.15	$210.10
Purchase #5	$35.37	7.874%	$38.155	$38.16	$38.15	$38.20
Purchase #6	$27.99	5.529%	$29.5376	$29.54	$29.55	$29.50
Purchase #7	$99.50	5.803%	$105.274	$105.27	$105.25	$105.30
7 purchase totals =	$549.24		$592.9088	$592.91	$592.90	$592.90