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	$141.90	4.363%	$148.0911	$148.09	$148.10	$148.10
Purchase #2	$204.31	11.694%	$228.202	$228.20	$228.20	$228.20
Purchase #3	$41.28	10.129%	$45.4613	$45.46	$45.45	$45.50
Purchase #4	$86.92	3.368%	$89.8475	$89.85	$89.85	$89.80
Purchase #5	$185.93	6.793%	$198.5602	$198.56	$198.55	$198.60
Purchase #6	$59.81	10.219%	$65.922	$65.92	$65.90	$65.90
Purchase #7	$186.27	6.485%	$198.3496	$198.35	$198.35	$198.30
7 purchase totals =	$906.42		$974.4337	$974.43	$974.40	$974.40