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	$125.73	8.761%	$136.7452	$136.75	$136.75	$136.70
Purchase #2	$116.99	9.284%	$127.8514	$127.85	$127.85	$127.90
Purchase #3	$205.34	3.728%	$212.9951	$213.00	$213.00	$213.00
Purchase #4	$55.62	6.333%	$59.1424	$59.14	$59.15	$59.10
Purchase #5	$146.89	4.869%	$154.0421	$154.04	$154.05	$154.00
Purchase #6	$138.75	7.274%	$148.8427	$148.84	$148.85	$148.80
Purchase #7	$84.71	5.168%	$89.0878	$89.09	$89.10	$89.10
7 purchase totals =	$874.03		$928.7067	$928.71	$928.75	$928.60