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	$28.47	11.867%	$31.8485	$31.85	$31.85	$31.80
Purchase #2	$246.37	3.808%	$255.7518	$255.75	$255.75	$255.80
Purchase #3	$79.80	5.163%	$83.9201	$83.92	$83.90	$83.90
Purchase #4	$151.71	9.460%	$166.0618	$166.06	$166.05	$166.10
Purchase #5	$141.86	6.700%	$151.3646	$151.36	$151.35	$151.40
Purchase #6	$90.44	12.658%	$101.8879	$101.89	$101.90	$101.90
Purchase #7	$202.37	13.861%	$230.4205	$230.42	$230.40	$230.40
7 purchase totals =	$941.02		$1,021.2552	$1,021.25	$1,021.20	$1,021.30