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	$49.46	10.385%	$54.5964	$54.60	$54.60	$54.60
Purchase #2	$35.26	9.416%	$38.5801	$38.58	$38.60	$38.60
Purchase #3	$172.43	5.440%	$181.8102	$181.81	$181.80	$181.80
Purchase #4	$78.52	9.292%	$85.8161	$85.82	$85.80	$85.80
Purchase #5	$91.54	3.428%	$94.678	$94.68	$94.70	$94.70
Purchase #6	$106.31	5.260%	$111.9019	$111.90	$111.90	$111.90
Purchase #7	$96.99	4.450%	$101.3061	$101.31	$101.30	$101.30
7 purchase totals =	$630.51		$668.6888	$668.70	$668.70	$668.70