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	$79.46	12.329%	$89.2566	$89.26	$89.25	$89.30
Purchase #2	$235.26	13.172%	$266.2484	$266.25	$266.25	$266.20
Purchase #3	$98.69	7.240%	$105.8352	$105.84	$105.85	$105.80
Purchase #4	$194.81	12.633%	$219.4203	$219.42	$219.40	$219.40
Purchase #5	$205.97	5.812%	$217.941	$217.94	$217.95	$217.90
Purchase #6	$65.38	11.505%	$72.902	$72.90	$72.90	$72.90
Purchase #7	$157.62	13.735%	$179.2691	$179.27	$179.25	$179.30
7 purchase totals =	$1,037.19		$1,150.8726	$1,150.88	$1,150.85	$1,150.80