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	$20.40	5.856%	$21.5946	$21.59	$21.60	$21.60
Purchase #2	$160.39	7.807%	$172.9116	$172.91	$172.90	$172.90
Purchase #3	$105.85	11.819%	$118.3604	$118.36	$118.35	$118.40
Purchase #4	$16.33	7.316%	$17.5247	$17.52	$17.50	$17.50
Purchase #5	$63.55	9.374%	$69.5072	$69.51	$69.50	$69.50
Purchase #6	$6.84	5.607%	$7.2235	$7.22	$7.20	$7.20
Purchase #7	$91.47	9.466%	$100.1286	$100.13	$100.15	$100.10
7 purchase totals =	$464.83		$507.2506	$507.24	$507.20	$507.20