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	$218.72	10.304%	$241.2569	$241.26	$241.25	$241.30
Purchase #2	$118.79	4.479%	$124.1106	$124.11	$124.10	$124.10
Purchase #3	$131.51	7.535%	$141.4193	$141.42	$141.40	$141.40
Purchase #4	$45.65	13.411%	$51.7721	$51.77	$51.75	$51.80
Purchase #5	$10.82	4.389%	$11.2949	$11.29	$11.30	$11.30
Purchase #6	$56.47	4.155%	$58.8163	$58.82	$58.80	$58.80
Purchase #7	$158.36	8.168%	$171.2948	$171.29	$171.30	$171.30
7 purchase totals =	$740.32		$799.9649	$799.96	$799.90	$800.00