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	$81.96	12.593%	$92.2812	$92.28	$92.30	$92.30
Purchase #2	$73.82	12.646%	$83.1553	$83.16	$83.15	$83.20
Purchase #3	$84.54	9.499%	$92.5705	$92.57	$92.55	$92.60
Purchase #4	$151.95	5.685%	$160.5884	$160.59	$160.60	$160.60
Purchase #5	$67.58	3.627%	$70.0311	$70.03	$70.05	$70.00
Purchase #6	$81.95	9.529%	$89.759	$89.76	$89.75	$89.80
Purchase #7	$247.60	9.803%	$271.8722	$271.87	$271.85	$271.90
7 purchase totals =	$789.40		$860.2577	$860.26	$860.25	$860.40