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	$53.80	13.474%	$61.049	$61.05	$61.05	$61.00
Purchase #2	$141.30	11.189%	$157.1101	$157.11	$157.10	$157.10
Purchase #3	$88.53	10.254%	$97.6079	$97.61	$97.60	$97.60
Purchase #4	$58.36	6.131%	$61.9381	$61.94	$61.95	$61.90
Purchase #5	$171.87	4.315%	$179.2862	$179.29	$179.30	$179.30
Purchase #6	$55.76	7.459%	$59.9191	$59.92	$59.90	$59.90
Purchase #7	$20.62	11.269%	$22.9437	$22.94	$22.95	$22.90
7 purchase totals =	$590.24		$639.8541	$639.86	$639.85	$639.70