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	$128.34	12.368%	$144.2131	$144.21	$144.20	$144.20
Purchase #2	$106.93	4.221%	$111.4435	$111.44	$111.45	$111.40
Purchase #3	$183.50	8.476%	$199.0535	$199.05	$199.05	$199.10
Purchase #4	$86.97	10.534%	$96.1314	$96.13	$96.15	$96.10
Purchase #5	$100.94	4.872%	$105.8578	$105.86	$105.85	$105.90
Purchase #6	$221.51	3.787%	$229.8986	$229.90	$229.90	$229.90
Purchase #7	$35.99	13.652%	$40.9034	$40.90	$40.90	$40.90
7 purchase totals =	$864.18		$927.5013	$927.49	$927.50	$927.50