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	$87.95	3.641%	$91.1523	$91.15	$91.15	$91.20
Purchase #2	$213.72	13.773%	$243.1557	$243.16	$243.15	$243.20
Purchase #3	$172.36	10.294%	$190.1027	$190.10	$190.10	$190.10
Purchase #4	$125.26	11.671%	$139.8791	$139.88	$139.90	$139.90
Purchase #5	$129.65	12.556%	$145.9289	$145.93	$145.95	$145.90
Purchase #6	$84.55	7.402%	$90.8084	$90.81	$90.80	$90.80
Purchase #7	$185.75	4.559%	$194.2183	$194.22	$194.20	$194.20
7 purchase totals =	$999.24		$1,095.2454	$1,095.25	$1,095.25	$1,095.30