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	$176.74	3.404%	$182.7562	$182.76	$182.75	$182.80
Purchase #2	$101.71	6.386%	$108.2052	$108.21	$108.20	$108.20
Purchase #3	$97.76	7.675%	$105.2631	$105.26	$105.25	$105.30
Purchase #4	$160.86	7.615%	$173.1095	$173.11	$173.10	$173.10
Purchase #5	$91.52	8.264%	$99.0832	$99.08	$99.10	$99.10
Purchase #6	$78.28	7.672%	$84.2856	$84.29	$84.30	$84.30
Purchase #7	$81.43	10.400%	$89.8987	$89.90	$89.90	$89.90
7 purchase totals =	$788.30		$842.6015	$842.61	$842.60	$842.70