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	$59.56	13.663%	$67.6977	$67.70	$67.70	$67.70
Purchase #2	$91.32	8.517%	$99.0977	$99.10	$99.10	$99.10
Purchase #3	$214.92	13.107%	$243.0896	$243.09	$243.10	$243.10
Purchase #4	$185.93	10.320%	$205.118	$205.12	$205.10	$205.10
Purchase #5	$197.38	8.220%	$213.6046	$213.60	$213.60	$213.60
Purchase #6	$153.80	4.858%	$161.2716	$161.27	$161.25	$161.30
Purchase #7	$123.72	5.483%	$130.5036	$130.50	$130.50	$130.50
7 purchase totals =	$1,026.63		$1,120.3828	$1,120.38	$1,120.35	$1,120.40