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	$50.67	8.866%	$55.1624	$55.16	$55.15	$55.20
Purchase #2	$160.79	6.819%	$171.7543	$171.75	$171.75	$171.80
Purchase #3	$18.46	7.283%	$19.8044	$19.80	$19.80	$19.80
Purchase #4	$84.57	5.672%	$89.3668	$89.37	$89.35	$89.40
Purchase #5	$85.81	12.132%	$96.2205	$96.22	$96.20	$96.20
Purchase #6	$114.41	11.795%	$127.9047	$127.90	$127.90	$127.90
Purchase #7	$54.36	12.676%	$61.2507	$61.25	$61.25	$61.30
7 purchase totals =	$569.07		$621.4638	$621.45	$621.40	$621.60