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	$41.68	9.106%	$45.4754	$45.48	$45.50	$45.50
Purchase #2	$193.63	3.356%	$200.1282	$200.13	$200.15	$200.10
Purchase #3	$148.29	13.859%	$168.8415	$168.84	$168.85	$168.80
Purchase #4	$5.27	12.478%	$5.9276	$5.93	$5.95	$5.90
Purchase #5	$35.26	6.619%	$37.5939	$37.59	$37.60	$37.60
Purchase #6	$66.47	7.733%	$71.6101	$71.61	$71.60	$71.60
Purchase #7	$36.71	9.623%	$40.2426	$40.24	$40.25	$40.20
7 purchase totals =	$527.31		$569.8193	$569.82	$569.90	$569.70