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	$35.28	11.727%	$39.4173	$39.42	$39.40	$39.40
Purchase #2	$249.81	5.308%	$263.0699	$263.07	$263.05	$263.10
Purchase #3	$198.82	7.583%	$213.8965	$213.90	$213.90	$213.90
Purchase #4	$226.48	8.140%	$244.9155	$244.92	$244.90	$244.90
Purchase #5	$74.36	11.137%	$82.6415	$82.64	$82.65	$82.60
Purchase #6	$112.91	6.731%	$120.51	$120.51	$120.50	$120.50
Purchase #7	$127.82	11.339%	$142.3135	$142.31	$142.30	$142.30
7 purchase totals =	$1,025.48		$1,106.7642	$1,106.77	$1,106.70	$1,106.70