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	$84.63	9.404%	$92.5886	$92.59	$92.60	$92.60
Purchase #2	$190.92	12.702%	$215.1707	$215.17	$215.15	$215.20
Purchase #3	$102.81	5.715%	$108.6856	$108.69	$108.70	$108.70
Purchase #4	$29.80	5.432%	$31.4187	$31.42	$31.40	$31.40
Purchase #5	$17.51	7.820%	$18.8793	$18.88	$18.90	$18.90
Purchase #6	$147.25	12.139%	$165.1247	$165.12	$165.10	$165.10
Purchase #7	$97.83	8.667%	$106.3089	$106.31	$106.30	$106.30
7 purchase totals =	$670.75		$738.1765	$738.18	$738.15	$738.20