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	$56.64	4.874%	$59.4006	$59.40	$59.40	$59.40
Purchase #2	$69.71	9.104%	$76.0564	$76.06	$76.05	$76.10
Purchase #3	$111.92	7.205%	$119.9838	$119.98	$120.00	$120.00
Purchase #4	$163.64	9.412%	$179.0418	$179.04	$179.05	$179.00
Purchase #5	$131.73	6.131%	$139.8064	$139.81	$139.80	$139.80
Purchase #6	$152.68	9.861%	$167.7358	$167.74	$167.75	$167.70
Purchase #7	$39.95	12.215%	$44.8299	$44.83	$44.85	$44.80
7 purchase totals =	$726.27		$786.8547	$786.86	$786.90	$786.80