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	$60.63	6.553%	$64.6031	$64.60	$64.60	$64.60
Purchase #2	$32.42	12.515%	$36.4774	$36.48	$36.50	$36.50
Purchase #3	$92.98	7.123%	$99.603	$99.60	$99.60	$99.60
Purchase #4	$81.70	8.408%	$88.5693	$88.57	$88.55	$88.60
Purchase #5	$98.65	3.859%	$102.4569	$102.46	$102.45	$102.50
Purchase #6	$204.87	11.587%	$228.6083	$228.61	$228.60	$228.60
Purchase #7	$150.34	3.765%	$156.0003	$156.00	$156.00	$156.00
7 purchase totals =	$721.59		$776.3183	$776.32	$776.30	$776.40