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	$124.73	7.307%	$133.844	$133.84	$133.85	$133.80
Purchase #2	$102.91	13.290%	$116.5867	$116.59	$116.60	$116.60
Purchase #3	$20.91	6.720%	$22.3152	$22.32	$22.30	$22.30
Purchase #4	$50.76	9.298%	$55.4797	$55.48	$55.50	$55.50
Purchase #5	$125.40	5.167%	$131.8794	$131.88	$131.90	$131.90
Purchase #6	$26.64	4.290%	$27.7829	$27.78	$27.80	$27.80
Purchase #7	$39.30	3.756%	$40.7761	$40.78	$40.80	$40.80
7 purchase totals =	$490.65		$528.6640	$528.67	$528.75	$528.70