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	$248.73	12.106%	$278.8413	$278.84	$278.85	$278.80
Purchase #2	$130.28	9.449%	$142.5902	$142.59	$142.60	$142.60
Purchase #3	$192.99	7.140%	$206.7695	$206.77	$206.75	$206.80
Purchase #4	$57.66	6.435%	$61.3704	$61.37	$61.35	$61.40
Purchase #5	$78.75	4.264%	$82.1079	$82.11	$82.10	$82.10
Purchase #6	$119.43	7.738%	$128.6715	$128.67	$128.65	$128.70
Purchase #7	$52.64	6.201%	$55.9042	$55.90	$55.90	$55.90
7 purchase totals =	$880.48		$956.2550	$956.25	$956.20	$956.30