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	$122.59	13.842%	$139.5589	$139.56	$139.55	$139.60
Purchase #2	$37.50	12.869%	$42.3259	$42.33	$42.35	$42.30
Purchase #3	$217.97	9.226%	$238.0799	$238.08	$238.10	$238.10
Purchase #4	$19.89	11.465%	$22.1704	$22.17	$22.15	$22.20
Purchase #5	$19.91	10.573%	$22.0151	$22.02	$22.00	$22.00
Purchase #6	$156.45	9.635%	$171.524	$171.52	$171.50	$171.50
Purchase #7	$34.88	13.715%	$39.6638	$39.66	$39.65	$39.70
7 purchase totals =	$609.19		$675.3380	$675.34	$675.30	$675.40