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	$5.34	4.621%	$5.5868	$5.59	$5.60	$5.60
Purchase #2	$79.80	11.653%	$89.0991	$89.10	$89.10	$89.10
Purchase #3	$246.78	4.275%	$257.3298	$257.33	$257.35	$257.30
Purchase #4	$161.75	6.207%	$171.7898	$171.79	$171.80	$171.80
Purchase #5	$37.69	7.131%	$40.3777	$40.38	$40.40	$40.40
Purchase #6	$87.82	12.224%	$98.5551	$98.56	$98.55	$98.60
Purchase #7	$131.66	9.397%	$144.0321	$144.03	$144.05	$144.00
7 purchase totals =	$750.84		$806.7704	$806.78	$806.85	$806.80