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	$76.83	4.551%	$80.3265	$80.33	$80.35	$80.30
Purchase #2	$185.39	3.633%	$192.1252	$192.13	$192.15	$192.10
Purchase #3	$88.96	12.789%	$100.3371	$100.34	$100.35	$100.30
Purchase #4	$96.64	3.637%	$100.1548	$100.15	$100.15	$100.20
Purchase #5	$109.43	8.331%	$118.5466	$118.55	$118.55	$118.50
Purchase #6	$142.90	12.111%	$160.2066	$160.21	$160.20	$160.20
Purchase #7	$100.98	6.523%	$107.5669	$107.57	$107.55	$107.60
7 purchase totals =	$801.13		$859.2637	$859.28	$859.30	$859.20