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	$159.27	6.115%	$169.0094	$169.01	$169.00	$169.00
Purchase #2	$192.53	12.456%	$216.5115	$216.51	$216.50	$216.50
Purchase #3	$72.70	13.689%	$82.6519	$82.65	$82.65	$82.70
Purchase #4	$165.38	4.109%	$172.1755	$172.18	$172.20	$172.20
Purchase #5	$23.94	11.516%	$26.6969	$26.70	$26.70	$26.70
Purchase #6	$99.36	12.178%	$111.4601	$111.46	$111.45	$111.50
Purchase #7	$87.56	9.311%	$95.7127	$95.71	$95.70	$95.70
7 purchase totals =	$800.74		$874.2180	$874.22	$874.20	$874.30