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	$149.84	12.222%	$168.1534	$168.15	$168.15	$168.20
Purchase #2	$200.98	8.843%	$218.7527	$218.75	$218.75	$218.80
Purchase #3	$111.95	10.440%	$123.6376	$123.64	$123.65	$123.60
Purchase #4	$92.72	5.793%	$98.0913	$98.09	$98.10	$98.10
Purchase #5	$166.51	3.556%	$172.4311	$172.43	$172.45	$172.40
Purchase #6	$36.36	8.846%	$39.5764	$39.58	$39.60	$39.60
Purchase #7	$124.92	12.611%	$140.6737	$140.67	$140.65	$140.70
7 purchase totals =	$883.28		$961.3162	$961.31	$961.35	$961.40