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	$83.94	6.518%	$89.4112	$89.41	$89.40	$89.40
Purchase #2	$36.56	11.686%	$40.8324	$40.83	$40.85	$40.80
Purchase #3	$33.34	5.821%	$35.2807	$35.28	$35.30	$35.30
Purchase #4	$156.40	7.327%	$167.8594	$167.86	$167.85	$167.90
Purchase #5	$31.31	6.630%	$33.3859	$33.39	$33.40	$33.40
Purchase #6	$64.92	6.519%	$69.1521	$69.15	$69.15	$69.20
Purchase #7	$138.86	5.586%	$146.6167	$146.62	$146.60	$146.60
7 purchase totals =	$545.33		$582.5384	$582.54	$582.55	$582.60