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	$36.51	10.159%	$40.2191	$40.22	$40.20	$40.20
Purchase #2	$206.48	10.240%	$227.6236	$227.62	$227.60	$227.60
Purchase #3	$242.87	3.313%	$250.9163	$250.92	$250.90	$250.90
Purchase #4	$69.96	8.382%	$75.824	$75.82	$75.80	$75.80
Purchase #5	$100.86	10.463%	$111.413	$111.41	$111.40	$111.40
Purchase #6	$195.87	7.588%	$210.7326	$210.73	$210.75	$210.70
Purchase #7	$24.58	5.195%	$25.8569	$25.86	$25.85	$25.90
7 purchase totals =	$877.13		$942.5855	$942.58	$942.50	$942.50