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	$220.34	3.616%	$228.3075	$228.31	$228.30	$228.30
Purchase #2	$91.79	13.782%	$104.4405	$104.44	$104.45	$104.40
Purchase #3	$83.91	7.197%	$89.949	$89.95	$89.95	$89.90
Purchase #4	$172.25	4.424%	$179.8703	$179.87	$179.85	$179.90
Purchase #5	$142.86	9.695%	$156.7103	$156.71	$156.70	$156.70
Purchase #6	$191.93	7.243%	$205.8315	$205.83	$205.85	$205.80
Purchase #7	$35.32	12.788%	$39.8367	$39.84	$39.85	$39.80
7 purchase totals =	$938.40		$1,004.9458	$1,004.95	$1,004.95	$1,004.80