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	$154.53	9.271%	$168.8565	$168.86	$168.85	$168.90
Purchase #2	$234.84	4.521%	$245.4571	$245.46	$245.45	$245.50
Purchase #3	$41.39	9.263%	$45.224	$45.22	$45.20	$45.20
Purchase #4	$154.59	9.180%	$168.7814	$168.78	$168.80	$168.80
Purchase #5	$233.78	5.312%	$246.1984	$246.20	$246.20	$246.20
Purchase #6	$149.92	5.451%	$158.0921	$158.09	$158.10	$158.10
Purchase #7	$60.74	11.524%	$67.7397	$67.74	$67.75	$67.70
7 purchase totals =	$1,029.79		$1,100.3492	$1,100.35	$1,100.35	$1,100.40