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	$89.34	11.394%	$99.5194	$99.52	$99.50	$99.50
Purchase #2	$90.76	7.251%	$97.341	$97.34	$97.35	$97.30
Purchase #3	$105.81	10.570%	$116.9941	$116.99	$117.00	$117.00
Purchase #4	$162.46	5.421%	$171.267	$171.27	$171.25	$171.30
Purchase #5	$67.68	8.380%	$73.3516	$73.35	$73.35	$73.40
Purchase #6	$66.49	10.549%	$73.504	$73.50	$73.50	$73.50
Purchase #7	$7.29	6.238%	$7.7448	$7.74	$7.75	$7.70
7 purchase totals =	$589.83		$639.7219	$639.71	$639.70	$639.70