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	$134.62	7.318%	$144.4715	$144.47	$144.45	$144.50
Purchase #2	$109.68	4.514%	$114.631	$114.63	$114.65	$114.60
Purchase #3	$90.89	5.757%	$96.1225	$96.12	$96.10	$96.10
Purchase #4	$127.57	10.161%	$140.5324	$140.53	$140.55	$140.50
Purchase #5	$57.82	3.322%	$59.7408	$59.74	$59.75	$59.70
Purchase #6	$212.41	11.755%	$237.3788	$237.38	$237.40	$237.40
Purchase #7	$36.83	8.414%	$39.9289	$39.93	$39.95	$39.90
7 purchase totals =	$769.82		$832.8059	$832.80	$832.85	$832.70