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	$155.71	12.254%	$174.7907	$174.79	$174.80	$174.80
Purchase #2	$190.36	12.257%	$213.6924	$213.69	$213.70	$213.70
Purchase #3	$220.92	10.804%	$244.7882	$244.79	$244.80	$244.80
Purchase #4	$61.28	10.340%	$67.6164	$67.62	$67.60	$67.60
Purchase #5	$210.36	3.235%	$217.1651	$217.17	$217.15	$217.20
Purchase #6	$228.47	12.282%	$256.5307	$256.53	$256.55	$256.50
Purchase #7	$99.72	13.227%	$112.91	$112.91	$112.90	$112.90
7 purchase totals =	$1,166.82		$1,287.4935	$1,287.50	$1,287.50	$1,287.50