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	$153.57	9.547%	$168.2313	$168.23	$168.25	$168.20
Purchase #2	$156.87	5.443%	$165.4084	$165.41	$165.40	$165.40
Purchase #3	$169.44	10.266%	$186.8347	$186.83	$186.85	$186.80
Purchase #4	$203.62	3.582%	$210.9137	$210.91	$210.90	$210.90
Purchase #5	$52.69	10.160%	$58.0433	$58.04	$58.05	$58.00
Purchase #6	$118.47	8.448%	$128.4783	$128.48	$128.50	$128.50
Purchase #7	$173.49	3.450%	$179.4754	$179.48	$179.50	$179.50
7 purchase totals =	$1,028.15		$1,097.3851	$1,097.38	$1,097.45	$1,097.30