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	$34.92	7.253%	$37.4527	$37.45	$37.45	$37.50
Purchase #2	$128.54	12.869%	$145.0818	$145.08	$145.10	$145.10
Purchase #3	$120.93	11.651%	$135.0196	$135.02	$135.00	$135.00
Purchase #4	$44.36	4.836%	$46.5052	$46.51	$46.50	$46.50
Purchase #5	$82.77	8.227%	$89.5795	$89.58	$89.60	$89.60
Purchase #6	$131.38	8.355%	$142.3568	$142.36	$142.35	$142.40
Purchase #7	$117.93	9.214%	$128.7961	$128.80	$128.80	$128.80
7 purchase totals =	$660.83		$724.7917	$724.80	$724.80	$724.90