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	$198.41	10.160%	$218.5685	$218.57	$218.55	$218.60
Purchase #2	$81.52	12.734%	$91.9008	$91.90	$91.90	$91.90
Purchase #3	$36.73	11.249%	$40.8618	$40.86	$40.85	$40.90
Purchase #4	$72.41	13.612%	$82.2664	$82.27	$82.25	$82.30
Purchase #5	$111.50	9.166%	$121.7201	$121.72	$121.70	$121.70
Purchase #6	$151.50	5.324%	$159.5659	$159.57	$159.55	$159.60
Purchase #7	$61.25	12.625%	$68.9828	$68.98	$69.00	$69.00
7 purchase totals =	$713.32		$783.8663	$783.87	$783.80	$784.00