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	$91.56	8.320%	$99.1778	$99.18	$99.20	$99.20
Purchase #2	$76.34	3.194%	$78.7783	$78.78	$78.80	$78.80
Purchase #3	$79.85	11.863%	$89.3226	$89.32	$89.30	$89.30
Purchase #4	$91.30	3.704%	$94.6818	$94.68	$94.70	$94.70
Purchase #5	$228.84	10.530%	$252.9369	$252.94	$252.95	$252.90
Purchase #6	$191.81	9.272%	$209.5946	$209.59	$209.60	$209.60
Purchase #7	$53.76	11.347%	$59.8601	$59.86	$59.85	$59.90
7 purchase totals =	$813.46		$884.3521	$884.35	$884.40	$884.40