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	$21.46	5.862%	$22.718	$22.72	$22.70	$22.70
Purchase #2	$132.88	10.556%	$146.9068	$146.91	$146.90	$146.90
Purchase #3	$229.82	3.659%	$238.2291	$238.23	$238.25	$238.20
Purchase #4	$19.32	6.538%	$20.5831	$20.58	$20.60	$20.60
Purchase #5	$168.54	9.367%	$184.3271	$184.33	$184.35	$184.30
Purchase #6	$51.91	9.731%	$56.9614	$56.96	$56.95	$57.00
Purchase #7	$6.29	3.208%	$6.4918	$6.49	$6.50	$6.50
7 purchase totals =	$630.22		$676.2173	$676.22	$676.25	$676.20