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	$194.76	13.667%	$221.3778	$221.38	$221.40	$221.40
Purchase #2	$145.85	11.563%	$162.7146	$162.71	$162.70	$162.70
Purchase #3	$180.88	7.684%	$194.7788	$194.78	$194.80	$194.80
Purchase #4	$188.45	12.243%	$211.5219	$211.52	$211.50	$211.50
Purchase #5	$16.44	13.716%	$18.6949	$18.69	$18.70	$18.70
Purchase #6	$125.78	13.618%	$142.9087	$142.91	$142.90	$142.90
Purchase #7	$135.77	4.129%	$141.3759	$141.38	$141.40	$141.40
7 purchase totals =	$987.93		$1,093.3726	$1,093.37	$1,093.40	$1,093.40