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	$67.99	4.309%	$70.9197	$70.92	$70.90	$70.90
Purchase #2	$183.83	6.474%	$195.7312	$195.73	$195.75	$195.70
Purchase #3	$55.45	10.793%	$61.4347	$61.43	$61.45	$61.40
Purchase #4	$101.79	6.563%	$108.4705	$108.47	$108.45	$108.50
Purchase #5	$84.87	11.472%	$94.6063	$94.61	$94.60	$94.60
Purchase #6	$250.43	3.376%	$258.8845	$258.88	$258.90	$258.90
Purchase #7	$79.55	12.308%	$89.341	$89.34	$89.35	$89.30
7 purchase totals =	$823.91		$879.3879	$879.38	$879.40	$879.30