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	$96.78	3.155%	$99.8334	$99.83	$99.85	$99.80
Purchase #2	$160.97	5.196%	$169.334	$169.33	$169.35	$169.30
Purchase #3	$129.60	11.328%	$144.2811	$144.28	$144.30	$144.30
Purchase #4	$106.95	8.607%	$116.1552	$116.16	$116.15	$116.20
Purchase #5	$154.38	6.515%	$164.4379	$164.44	$164.45	$164.40
Purchase #6	$85.48	7.751%	$92.1056	$92.11	$92.10	$92.10
Purchase #7	$40.34	10.568%	$44.6031	$44.60	$44.60	$44.60
7 purchase totals =	$774.50		$830.7503	$830.75	$830.80	$830.70