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	$86.52	8.738%	$94.0801	$94.08	$94.10	$94.10
Purchase #2	$168.90	6.259%	$179.4715	$179.47	$179.45	$179.50
Purchase #3	$89.79	5.306%	$94.5543	$94.55	$94.55	$94.60
Purchase #4	$100.50	5.227%	$105.7531	$105.75	$105.75	$105.80
Purchase #5	$71.86	13.755%	$81.7443	$81.74	$81.75	$81.70
Purchase #6	$177.28	12.443%	$199.339	$199.34	$199.35	$199.30
Purchase #7	$71.35	10.556%	$78.8817	$78.88	$78.90	$78.90
7 purchase totals =	$766.20		$833.8240	$833.81	$833.85	$833.90