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	$105.91	4.596%	$110.7776	$110.78	$110.80	$110.80
Purchase #2	$26.27	4.861%	$27.547	$27.55	$27.55	$27.50
Purchase #3	$134.70	7.267%	$144.4886	$144.49	$144.50	$144.50
Purchase #4	$85.43	12.423%	$96.043	$96.04	$96.05	$96.00
Purchase #5	$33.28	11.835%	$37.2187	$37.22	$37.20	$37.20
Purchase #6	$54.30	4.254%	$56.6099	$56.61	$56.60	$56.60
Purchase #7	$62.72	9.201%	$68.4909	$68.49	$68.50	$68.50
7 purchase totals =	$502.61		$541.1757	$541.18	$541.20	$541.10