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	$16.83	11.570%	$18.7772	$18.78	$18.80	$18.80
Purchase #2	$137.67	7.272%	$147.6814	$147.68	$147.70	$147.70
Purchase #3	$38.34	5.258%	$40.3559	$40.36	$40.35	$40.40
Purchase #4	$96.63	9.658%	$105.9625	$105.96	$105.95	$106.00
Purchase #5	$20.71	7.365%	$22.2353	$22.24	$22.25	$22.20
Purchase #6	$199.76	11.141%	$222.0153	$222.02	$222.00	$222.00
Purchase #7	$59.57	9.749%	$65.3775	$65.38	$65.40	$65.40
7 purchase totals =	$569.51		$622.4051	$622.42	$622.45	$622.50