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	$11.72	5.512%	$12.366	$12.37	$12.35	$12.40
Purchase #2	$186.39	6.668%	$198.8185	$198.82	$198.80	$198.80
Purchase #3	$134.49	4.210%	$140.152	$140.15	$140.15	$140.20
Purchase #4	$100.48	11.570%	$112.1055	$112.11	$112.10	$112.10
Purchase #5	$93.56	6.762%	$99.8865	$99.89	$99.90	$99.90
Purchase #6	$14.72	7.160%	$15.774	$15.77	$15.75	$15.80
Purchase #7	$208.67	6.402%	$222.0291	$222.03	$222.05	$222.00
7 purchase totals =	$750.03		$801.1316	$801.14	$801.10	$801.20