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	$127.82	8.751%	$139.0055	$139.01	$139.00	$139.00
Purchase #2	$175.44	7.701%	$188.9506	$188.95	$188.95	$189.00
Purchase #3	$222.64	9.212%	$243.1496	$243.15	$243.15	$243.10
Purchase #4	$89.69	10.678%	$99.2671	$99.27	$99.25	$99.30
Purchase #5	$73.77	3.273%	$76.1845	$76.18	$76.20	$76.20
Purchase #6	$173.83	6.641%	$185.3741	$185.37	$185.35	$185.40
Purchase #7	$22.85	13.487%	$25.9318	$25.93	$25.95	$25.90
7 purchase totals =	$886.04		$957.8632	$957.86	$957.85	$957.90