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	$62.46	12.165%	$70.0583	$70.06	$70.05	$70.10
Purchase #2	$29.31	8.681%	$31.8544	$31.85	$31.85	$31.90
Purchase #3	$124.52	3.776%	$129.2219	$129.22	$129.20	$129.20
Purchase #4	$160.40	7.514%	$172.4525	$172.45	$172.45	$172.50
Purchase #5	$150.56	5.658%	$159.0787	$159.08	$159.10	$159.10
Purchase #6	$55.33	5.167%	$58.1889	$58.19	$58.20	$58.20
Purchase #7	$80.89	10.678%	$89.5274	$89.53	$89.55	$89.50
7 purchase totals =	$663.47		$710.3821	$710.38	$710.40	$710.50