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	$71.67	11.331%	$79.7909	$79.79	$79.80	$79.80
Purchase #2	$45.56	11.682%	$50.8823	$50.88	$50.90	$50.90
Purchase #3	$139.38	12.589%	$156.9265	$156.93	$156.95	$156.90
Purchase #4	$92.54	11.215%	$102.9184	$102.92	$102.90	$102.90
Purchase #5	$240.25	13.450%	$272.5636	$272.56	$272.55	$272.60
Purchase #6	$105.79	13.485%	$120.0558	$120.06	$120.05	$120.10
Purchase #7	$227.95	12.243%	$255.8579	$255.86	$255.85	$255.90
7 purchase totals =	$923.14		$1,038.9954	$1,039.00	$1,039.00	$1,039.10