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	$157.96	9.373%	$172.7656	$172.77	$172.75	$172.80
Purchase #2	$73.28	12.695%	$82.5829	$82.58	$82.60	$82.60
Purchase #3	$148.36	4.385%	$154.8656	$154.87	$154.85	$154.90
Purchase #4	$79.35	12.791%	$89.4997	$89.50	$89.50	$89.50
Purchase #5	$125.81	3.387%	$130.0712	$130.07	$130.05	$130.10
Purchase #6	$121.61	8.156%	$131.5285	$131.53	$131.55	$131.50
Purchase #7	$91.57	6.449%	$97.4753	$97.48	$97.50	$97.50
7 purchase totals =	$797.94		$858.7888	$858.80	$858.80	$858.90