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	$18.55	9.620%	$20.3345	$20.33	$20.35	$20.30
Purchase #2	$180.44	13.127%	$204.1264	$204.13	$204.15	$204.10
Purchase #3	$143.89	8.685%	$156.3868	$156.39	$156.40	$156.40
Purchase #4	$78.55	12.849%	$88.6429	$88.64	$88.65	$88.60
Purchase #5	$9.98	13.645%	$11.3418	$11.34	$11.35	$11.30
Purchase #6	$95.31	4.808%	$99.8925	$99.89	$99.90	$99.90
Purchase #7	$119.31	6.652%	$127.2465	$127.25	$127.25	$127.20
7 purchase totals =	$646.03		$707.9714	$707.97	$708.05	$707.80