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	$55.74	11.433%	$62.1128	$62.11	$62.10	$62.10
Purchase #2	$144.64	9.614%	$158.5457	$158.55	$158.55	$158.50
Purchase #3	$91.53	9.558%	$100.2784	$100.28	$100.30	$100.30
Purchase #4	$101.96	7.551%	$109.659	$109.66	$109.65	$109.70
Purchase #5	$109.53	3.685%	$113.5662	$113.57	$113.55	$113.60
Purchase #6	$56.57	4.439%	$59.0811	$59.08	$59.10	$59.10
Purchase #7	$67.36	3.420%	$69.6637	$69.66	$69.65	$69.70
7 purchase totals =	$627.33		$672.9069	$672.91	$672.90	$673.00