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	$79.45	12.511%	$89.39	$89.39	$89.40	$89.40
Purchase #2	$18.54	10.669%	$20.518	$20.52	$20.50	$20.50
Purchase #3	$116.63	6.312%	$123.9917	$123.99	$124.00	$124.00
Purchase #4	$101.66	3.301%	$105.0158	$105.02	$105.00	$105.00
Purchase #5	$102.84	10.773%	$113.919	$113.92	$113.90	$113.90
Purchase #6	$242.50	10.530%	$268.0353	$268.04	$268.05	$268.00
Purchase #7	$121.44	10.280%	$133.924	$133.92	$133.90	$133.90
7 purchase totals =	$783.06		$854.7938	$854.80	$854.75	$854.70