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	$131.70	4.211%	$137.2459	$137.25	$137.25	$137.20
Purchase #2	$207.96	4.426%	$217.1643	$217.16	$217.15	$217.20
Purchase #3	$80.40	9.497%	$88.0356	$88.04	$88.05	$88.00
Purchase #4	$81.53	9.380%	$89.1775	$89.18	$89.20	$89.20
Purchase #5	$166.96	4.505%	$174.4815	$174.48	$174.50	$174.50
Purchase #6	$157.33	9.599%	$172.4321	$172.43	$172.45	$172.40
Purchase #7	$60.66	13.266%	$68.7072	$68.71	$68.70	$68.70
7 purchase totals =	$886.54		$947.2441	$947.25	$947.30	$947.20