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	$85.63	4.604%	$89.5724	$89.57	$89.55	$89.60
Purchase #2	$27.92	3.116%	$28.79	$28.79	$28.80	$28.80
Purchase #3	$161.93	6.259%	$172.0652	$172.07	$172.05	$172.10
Purchase #4	$7.89	12.116%	$8.846	$8.85	$8.85	$8.80
Purchase #5	$173.40	6.555%	$184.7664	$184.77	$184.75	$184.80
Purchase #6	$188.59	13.831%	$214.6739	$214.67	$214.65	$214.70
Purchase #7	$139.27	6.179%	$147.8755	$147.88	$147.90	$147.90
7 purchase totals =	$784.63		$846.5894	$846.60	$846.55	$846.70