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	$181.70	3.472%	$188.0086	$188.01	$188.00	$188.00
Purchase #2	$110.54	5.139%	$116.2207	$116.22	$116.20	$116.20
Purchase #3	$19.46	12.869%	$21.9643	$21.96	$21.95	$22.00
Purchase #4	$227.77	4.845%	$238.8055	$238.81	$238.80	$238.80
Purchase #5	$93.85	6.604%	$100.0479	$100.05	$100.05	$100.00
Purchase #6	$145.83	12.722%	$164.3825	$164.38	$164.40	$164.40
Purchase #7	$137.54	3.732%	$142.673	$142.67	$142.65	$142.70
7 purchase totals =	$916.69		$972.1025	$972.10	$972.05	$972.10