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	$90.74	10.641%	$100.3956	$100.40	$100.40	$100.40
Purchase #2	$180.36	10.835%	$199.902	$199.90	$199.90	$199.90
Purchase #3	$96.83	7.205%	$103.8066	$103.81	$103.80	$103.80
Purchase #4	$102.52	3.164%	$105.7637	$105.76	$105.75	$105.80
Purchase #5	$41.73	11.837%	$46.6696	$46.67	$46.65	$46.70
Purchase #6	$220.27	3.800%	$228.6403	$228.64	$228.65	$228.60
Purchase #7	$59.52	3.722%	$61.7353	$61.74	$61.75	$61.70
7 purchase totals =	$791.97		$846.9131	$846.92	$846.90	$846.90