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	$245.32	12.120%	$275.0528	$275.05	$275.05	$275.10
Purchase #2	$61.48	7.204%	$65.909	$65.91	$65.90	$65.90
Purchase #3	$24.65	6.188%	$26.1753	$26.18	$26.20	$26.20
Purchase #4	$120.87	5.322%	$127.3027	$127.30	$127.30	$127.30
Purchase #5	$83.72	3.765%	$86.8721	$86.87	$86.85	$86.90
Purchase #6	$59.32	13.402%	$67.2701	$67.27	$67.25	$67.30
Purchase #7	$167.25	7.308%	$179.4726	$179.47	$179.45	$179.50
7 purchase totals =	$762.61		$828.0546	$828.05	$828.00	$828.20