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	$84.45	6.405%	$89.859	$89.86	$89.85	$89.90
Purchase #2	$28.60	13.351%	$32.4184	$32.42	$32.40	$32.40
Purchase #3	$196.32	9.669%	$215.3022	$215.30	$215.30	$215.30
Purchase #4	$11.50	4.102%	$11.9717	$11.97	$11.95	$12.00
Purchase #5	$55.31	13.107%	$62.5595	$62.56	$62.55	$62.60
Purchase #6	$212.59	5.568%	$224.427	$224.43	$224.45	$224.40
Purchase #7	$219.42	11.710%	$245.1141	$245.11	$245.10	$245.10
7 purchase totals =	$808.19		$881.6519	$881.65	$881.60	$881.70