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	$6.72	12.530%	$7.562	$7.56	$7.55	$7.60
Purchase #2	$237.97	7.385%	$255.5441	$255.54	$255.55	$255.50
Purchase #3	$114.82	5.827%	$121.5106	$121.51	$121.50	$121.50
Purchase #4	$102.83	3.492%	$106.4208	$106.42	$106.40	$106.40
Purchase #5	$159.34	3.840%	$165.4587	$165.46	$165.45	$165.50
Purchase #6	$41.93	4.450%	$43.7959	$43.80	$43.80	$43.80
Purchase #7	$120.38	5.649%	$127.1803	$127.18	$127.20	$127.20
7 purchase totals =	$783.99		$827.4724	$827.47	$827.45	$827.50