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	$40.56	12.312%	$45.5537	$45.55	$45.55	$45.60
Purchase #2	$245.99	10.221%	$271.1326	$271.13	$271.15	$271.10
Purchase #3	$86.47	9.426%	$94.6207	$94.62	$94.60	$94.60
Purchase #4	$72.60	4.302%	$75.7233	$75.72	$75.70	$75.70
Purchase #5	$63.31	3.590%	$65.5828	$65.58	$65.60	$65.60
Purchase #6	$187.32	10.285%	$206.5859	$206.59	$206.60	$206.60
Purchase #7	$113.78	11.804%	$127.2106	$127.21	$127.20	$127.20
7 purchase totals =	$810.03		$886.4096	$886.40	$886.40	$886.40