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	$15.37	5.477%	$16.2118	$16.21	$16.20	$16.20
Purchase #2	$88.37	12.426%	$99.3509	$99.35	$99.35	$99.40
Purchase #3	$119.69	3.710%	$124.1305	$124.13	$124.15	$124.10
Purchase #4	$141.80	10.674%	$156.9357	$156.94	$156.95	$156.90
Purchase #5	$89.81	10.541%	$99.2769	$99.28	$99.30	$99.30
Purchase #6	$230.90	7.321%	$247.8042	$247.80	$247.80	$247.80
Purchase #7	$174.34	12.690%	$196.4637	$196.46	$196.45	$196.50
7 purchase totals =	$860.28		$940.1737	$940.17	$940.20	$940.20