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	$55.77	12.672%	$62.8372	$62.84	$62.85	$62.80
Purchase #2	$74.82	4.693%	$78.3313	$78.33	$78.35	$78.30
Purchase #3	$134.85	13.738%	$153.3757	$153.38	$153.40	$153.40
Purchase #4	$104.79	5.277%	$110.3198	$110.32	$110.30	$110.30
Purchase #5	$55.84	12.767%	$62.9691	$62.97	$62.95	$63.00
Purchase #6	$109.43	3.248%	$112.9843	$112.98	$113.00	$113.00
Purchase #7	$100.32	3.228%	$103.5583	$103.56	$103.55	$103.60
7 purchase totals =	$635.82		$684.3757	$684.38	$684.40	$684.40