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	$80.57	6.111%	$85.4936	$85.49	$85.50	$85.50
Purchase #2	$6.38	11.279%	$7.0996	$7.10	$7.10	$7.10
Purchase #3	$18.57	7.106%	$19.8896	$19.89	$19.90	$19.90
Purchase #4	$164.88	8.663%	$179.1636	$179.16	$179.15	$179.20
Purchase #5	$82.81	8.609%	$89.9391	$89.94	$89.95	$89.90
Purchase #6	$118.85	6.226%	$126.2496	$126.25	$126.25	$126.20
Purchase #7	$172.76	3.324%	$178.5025	$178.50	$178.50	$178.50
7 purchase totals =	$644.82		$686.3376	$686.33	$686.35	$686.30