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	$79.95	12.486%	$89.9326	$89.93	$89.95	$89.90
Purchase #2	$73.54	5.506%	$77.5891	$77.59	$77.60	$77.60
Purchase #3	$36.41	13.511%	$41.3294	$41.33	$41.35	$41.30
Purchase #4	$30.38	11.432%	$33.853	$33.85	$33.85	$33.90
Purchase #5	$177.59	3.545%	$183.8856	$183.89	$183.90	$183.90
Purchase #6	$201.87	5.387%	$212.7447	$212.74	$212.75	$212.70
Purchase #7	$63.94	3.125%	$65.9381	$65.94	$65.95	$65.90
7 purchase totals =	$663.68		$705.2725	$705.27	$705.35	$705.20