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	$93.62	12.263%	$105.1006	$105.10	$105.10	$105.10
Purchase #2	$154.54	7.241%	$165.7302	$165.73	$165.75	$165.70
Purchase #3	$82.44	10.783%	$91.3295	$91.33	$91.35	$91.30
Purchase #4	$70.38	12.678%	$79.3028	$79.30	$79.30	$79.30
Purchase #5	$25.97	6.333%	$27.6147	$27.61	$27.60	$27.60
Purchase #6	$200.58	12.427%	$225.5061	$225.51	$225.50	$225.50
Purchase #7	$132.67	9.152%	$144.812	$144.81	$144.80	$144.80
7 purchase totals =	$760.20		$839.3959	$839.39	$839.40	$839.30