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	$250.61	10.820%	$277.726	$277.73	$277.75	$277.70
Purchase #2	$81.99	9.147%	$89.4896	$89.49	$89.50	$89.50
Purchase #3	$231.38	6.701%	$246.8848	$246.88	$246.90	$246.90
Purchase #4	$56.59	4.464%	$59.1162	$59.12	$59.10	$59.10
Purchase #5	$74.57	6.362%	$79.3141	$79.31	$79.30	$79.30
Purchase #6	$170.60	5.353%	$179.7322	$179.73	$179.75	$179.70
Purchase #7	$25.90	9.260%	$28.2983	$28.30	$28.30	$28.30
7 purchase totals =	$891.64		$960.5612	$960.56	$960.60	$960.50