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	$170.61	10.280%	$188.1487	$188.15	$188.15	$188.10
Purchase #2	$8.43	10.305%	$9.2987	$9.30	$9.30	$9.30
Purchase #3	$94.96	4.773%	$99.4924	$99.49	$99.50	$99.50
Purchase #4	$35.83	4.657%	$37.4986	$37.50	$37.50	$37.50
Purchase #5	$238.98	4.690%	$250.1882	$250.19	$250.20	$250.20
Purchase #6	$158.59	12.804%	$178.8959	$178.90	$178.90	$178.90
Purchase #7	$153.42	3.563%	$158.8864	$158.89	$158.90	$158.90
7 purchase totals =	$860.82		$922.4089	$922.42	$922.45	$922.40