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	$205.48	12.351%	$230.8588	$230.86	$230.85	$230.90
Purchase #2	$107.44	3.597%	$111.3046	$111.30	$111.30	$111.30
Purchase #3	$104.31	10.698%	$115.4691	$115.47	$115.45	$115.50
Purchase #4	$101.88	3.763%	$105.7137	$105.71	$105.70	$105.70
Purchase #5	$88.43	9.115%	$96.4904	$96.49	$96.50	$96.50
Purchase #6	$75.48	10.678%	$83.5398	$83.54	$83.55	$83.50
Purchase #7	$46.36	6.718%	$49.4745	$49.47	$49.45	$49.50
7 purchase totals =	$729.38		$792.8509	$792.84	$792.80	$792.90