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	$210.89	11.338%	$234.8007	$234.80	$234.80	$234.80
Purchase #2	$59.33	8.664%	$64.4704	$64.47	$64.45	$64.50
Purchase #3	$83.33	7.491%	$89.5723	$89.57	$89.55	$89.60
Purchase #4	$17.31	4.259%	$18.0472	$18.05	$18.05	$18.00
Purchase #5	$99.26	12.500%	$111.6675	$111.67	$111.65	$111.70
Purchase #6	$179.72	7.709%	$193.5746	$193.57	$193.55	$193.60
Purchase #7	$148.98	12.664%	$167.8468	$167.85	$167.85	$167.80
7 purchase totals =	$798.82		$879.9795	$879.98	$879.90	$880.00