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	$172.46	8.710%	$187.4813	$187.48	$187.50	$187.50
Purchase #2	$34.93	6.535%	$37.2127	$37.21	$37.20	$37.20
Purchase #3	$250.82	8.765%	$272.8044	$272.80	$272.80	$272.80
Purchase #4	$169.33	6.773%	$180.7987	$180.80	$180.80	$180.80
Purchase #5	$115.53	10.383%	$127.5255	$127.53	$127.55	$127.50
Purchase #6	$246.43	11.660%	$275.1637	$275.16	$275.15	$275.20
Purchase #7	$25.77	9.272%	$28.1594	$28.16	$28.15	$28.20
7 purchase totals =	$1,015.27		$1,109.1457	$1,109.14	$1,109.15	$1,109.20