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	$55.32	11.866%	$61.8843	$61.88	$61.90	$61.90
Purchase #2	$231.40	6.271%	$245.9111	$245.91	$245.90	$245.90
Purchase #3	$145.46	5.115%	$152.9003	$152.90	$152.90	$152.90
Purchase #4	$50.50	3.703%	$52.37	$52.37	$52.35	$52.40
Purchase #5	$90.87	5.830%	$96.1677	$96.17	$96.15	$96.20
Purchase #6	$185.99	10.388%	$205.3106	$205.31	$205.30	$205.30
Purchase #7	$141.48	13.317%	$160.3209	$160.32	$160.30	$160.30
7 purchase totals =	$901.02		$974.8649	$974.86	$974.80	$974.90