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	$6.53	12.855%	$7.3694	$7.37	$7.35	$7.40
Purchase #2	$243.54	8.572%	$264.4162	$264.42	$264.40	$264.40
Purchase #3	$16.76	12.824%	$18.9093	$18.91	$18.90	$18.90
Purchase #4	$112.87	13.249%	$127.8241	$127.82	$127.80	$127.80
Purchase #5	$54.68	3.815%	$56.766	$56.77	$56.75	$56.80
Purchase #6	$208.37	3.609%	$215.8901	$215.89	$215.90	$215.90
Purchase #7	$31.41	8.216%	$33.9906	$33.99	$34.00	$34.00
7 purchase totals =	$674.16		$725.1657	$725.17	$725.10	$725.20