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	$81.42	10.427%	$89.9097	$89.91	$89.90	$89.90
Purchase #2	$59.36	7.169%	$63.6155	$63.62	$63.60	$63.60
Purchase #3	$139.70	9.827%	$153.4283	$153.43	$153.45	$153.40
Purchase #4	$58.99	9.205%	$64.42	$64.42	$64.40	$64.40
Purchase #5	$222.35	6.735%	$237.3253	$237.33	$237.35	$237.30
Purchase #6	$73.97	6.210%	$78.5635	$78.56	$78.55	$78.60
Purchase #7	$47.31	7.568%	$50.8904	$50.89	$50.90	$50.90
7 purchase totals =	$683.10		$738.1527	$738.16	$738.15	$738.10