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	$22.38	3.529%	$23.1698	$23.17	$23.15	$23.20
Purchase #2	$240.29	8.114%	$259.7871	$259.79	$259.80	$259.80
Purchase #3	$79.51	12.732%	$89.6332	$89.63	$89.65	$89.60
Purchase #4	$95.80	4.568%	$100.1761	$100.18	$100.20	$100.20
Purchase #5	$173.57	9.869%	$190.6996	$190.70	$190.70	$190.70
Purchase #6	$220.80	10.350%	$243.6528	$243.65	$243.65	$243.70
Purchase #7	$89.85	6.780%	$95.9418	$95.94	$95.95	$95.90
7 purchase totals =	$922.20		$1,003.0604	$1,003.06	$1,003.10	$1,003.10