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	$102.74	11.481%	$114.5356	$114.54	$114.55	$114.50
Purchase #2	$190.50	3.500%	$197.1675	$197.17	$197.15	$197.20
Purchase #3	$83.61	3.744%	$86.7404	$86.74	$86.75	$86.70
Purchase #4	$121.82	10.444%	$134.5429	$134.54	$134.55	$134.50
Purchase #5	$126.56	10.152%	$139.4084	$139.41	$139.40	$139.40
Purchase #6	$75.84	10.244%	$83.609	$83.61	$83.60	$83.60
Purchase #7	$61.38	5.112%	$64.5177	$64.52	$64.50	$64.50
7 purchase totals =	$762.45		$820.5215	$820.53	$820.50	$820.40