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	$99.91	6.699%	$106.603	$106.60	$106.60	$106.60
Purchase #2	$62.53	3.798%	$64.9049	$64.90	$64.90	$64.90
Purchase #3	$81.38	13.593%	$92.442	$92.44	$92.45	$92.40
Purchase #4	$127.38	11.499%	$142.0274	$142.03	$142.05	$142.00
Purchase #5	$53.82	6.404%	$57.2666	$57.27	$57.25	$57.30
Purchase #6	$136.34	4.331%	$142.2449	$142.24	$142.25	$142.20
Purchase #7	$98.54	5.653%	$104.1105	$104.11	$104.10	$104.10
7 purchase totals =	$659.90		$709.5993	$709.59	$709.60	$709.50