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	$36.32	13.673%	$41.286	$41.29	$41.30	$41.30
Purchase #2	$104.49	4.491%	$109.1826	$109.18	$109.20	$109.20
Purchase #3	$118.76	4.558%	$124.1731	$124.17	$124.15	$124.20
Purchase #4	$78.82	13.856%	$89.7413	$89.74	$89.75	$89.70
Purchase #5	$66.28	9.349%	$72.4765	$72.48	$72.50	$72.50
Purchase #6	$226.60	13.662%	$257.5581	$257.56	$257.55	$257.60
Purchase #7	$89.78	5.686%	$94.8849	$94.88	$94.90	$94.90
7 purchase totals =	$721.05		$789.3025	$789.30	$789.35	$789.40