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	$112.44	7.590%	$120.9742	$120.97	$120.95	$121.00
Purchase #2	$86.78	6.464%	$92.3895	$92.39	$92.40	$92.40
Purchase #3	$37.29	13.127%	$42.1851	$42.19	$42.20	$42.20
Purchase #4	$238.56	7.841%	$257.2655	$257.27	$257.25	$257.30
Purchase #5	$133.47	8.473%	$144.7789	$144.78	$144.80	$144.80
Purchase #6	$41.66	9.417%	$45.5831	$45.58	$45.60	$45.60
Purchase #7	$162.72	10.443%	$179.7128	$179.71	$179.70	$179.70
7 purchase totals =	$812.92		$882.8891	$882.89	$882.90	$883.00