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	$152.82	8.247%	$165.4231	$165.42	$165.40	$165.40
Purchase #2	$218.93	10.185%	$241.228	$241.23	$241.25	$241.20
Purchase #3	$89.77	10.436%	$99.1384	$99.14	$99.15	$99.10
Purchase #4	$164.50	3.458%	$170.1884	$170.19	$170.20	$170.20
Purchase #5	$213.77	4.238%	$222.8296	$222.83	$222.85	$222.80
Purchase #6	$65.42	10.814%	$72.4945	$72.49	$72.50	$72.50
Purchase #7	$185.83	12.548%	$209.1479	$209.15	$209.15	$209.10
7 purchase totals =	$1,091.04		$1,180.4499	$1,180.45	$1,180.50	$1,180.30