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	$221.32	11.139%	$245.9728	$245.97	$245.95	$246.00
Purchase #2	$111.68	5.518%	$117.8425	$117.84	$117.85	$117.80
Purchase #3	$104.65	6.531%	$111.4847	$111.48	$111.50	$111.50
Purchase #4	$73.67	5.599%	$77.7948	$77.79	$77.80	$77.80
Purchase #5	$124.89	8.709%	$135.7667	$135.77	$135.75	$135.80
Purchase #6	$78.93	13.239%	$89.3795	$89.38	$89.40	$89.40
Purchase #7	$59.54	3.843%	$61.8281	$61.83	$61.85	$61.80
7 purchase totals =	$774.68		$840.0691	$840.06	$840.10	$840.10