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	$167.97	10.331%	$185.323	$185.32	$185.30	$185.30
Purchase #2	$89.79	11.139%	$99.7917	$99.79	$99.80	$99.80
Purchase #3	$204.62	3.625%	$212.0375	$212.04	$212.05	$212.00
Purchase #4	$51.27	9.308%	$56.0422	$56.04	$56.05	$56.00
Purchase #5	$32.84	7.860%	$35.4212	$35.42	$35.40	$35.40
Purchase #6	$52.74	12.156%	$59.1511	$59.15	$59.15	$59.20
Purchase #7	$35.82	5.155%	$37.6665	$37.67	$37.65	$37.70
7 purchase totals =	$635.05		$685.4332	$685.43	$685.40	$685.40