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	$102.79	12.633%	$115.7755	$115.78	$115.80	$115.80
Purchase #2	$159.34	4.341%	$166.2569	$166.26	$166.25	$166.30
Purchase #3	$98.95	12.283%	$111.104	$111.10	$111.10	$111.10
Purchase #4	$103.74	8.722%	$112.7882	$112.79	$112.80	$112.80
Purchase #5	$245.72	7.356%	$263.7952	$263.80	$263.80	$263.80
Purchase #6	$159.42	13.207%	$180.4746	$180.47	$180.45	$180.50
Purchase #7	$117.35	11.849%	$131.2548	$131.25	$131.25	$131.30
7 purchase totals =	$987.31		$1,081.4492	$1,081.45	$1,081.45	$1,081.60