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	$78.50	3.220%	$81.0277	$81.03	$81.05	$81.00
Purchase #2	$20.87	3.809%	$21.6649	$21.66	$21.65	$21.70
Purchase #3	$151.57	4.192%	$157.9238	$157.92	$157.90	$157.90
Purchase #4	$140.46	8.642%	$152.5986	$152.60	$152.60	$152.60
Purchase #5	$60.34	8.264%	$65.3265	$65.33	$65.35	$65.30
Purchase #6	$163.25	5.515%	$172.2532	$172.25	$172.25	$172.30
Purchase #7	$15.52	6.343%	$16.5044	$16.50	$16.50	$16.50
7 purchase totals =	$630.51		$667.2991	$667.29	$667.30	$667.30