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	$16.35	11.663%	$18.2569	$18.26	$18.25	$18.30
Purchase #2	$49.73	10.613%	$55.0078	$55.01	$55.00	$55.00
Purchase #3	$205.77	13.387%	$233.3164	$233.32	$233.30	$233.30
Purchase #4	$199.55	9.416%	$218.3396	$218.34	$218.35	$218.30
Purchase #5	$56.42	3.329%	$58.2982	$58.30	$58.30	$58.30
Purchase #6	$250.59	3.318%	$258.9046	$258.90	$258.90	$258.90
Purchase #7	$92.87	7.809%	$100.1222	$100.12	$100.10	$100.10
7 purchase totals =	$871.28		$942.2457	$942.25	$942.20	$942.20