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	$22.71	11.840%	$25.3989	$25.40	$25.40	$25.40
Purchase #2	$89.89	3.317%	$92.8717	$92.87	$92.85	$92.90
Purchase #3	$42.64	6.388%	$45.3638	$45.36	$45.35	$45.40
Purchase #4	$161.86	10.685%	$179.1547	$179.15	$179.15	$179.20
Purchase #5	$182.91	13.104%	$206.8785	$206.88	$206.90	$206.90
Purchase #6	$81.94	12.127%	$91.8769	$91.88	$91.90	$91.90
Purchase #7	$10.70	5.333%	$11.2706	$11.27	$11.25	$11.30
7 purchase totals =	$592.65		$652.8151	$652.81	$652.80	$653.00