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	$165.40	10.508%	$182.7802	$182.78	$182.80	$182.80
Purchase #2	$72.98	12.841%	$82.3514	$82.35	$82.35	$82.40
Purchase #3	$90.57	6.541%	$96.4942	$96.49	$96.50	$96.50
Purchase #4	$84.93	11.405%	$94.6163	$94.62	$94.60	$94.60
Purchase #5	$121.25	5.168%	$127.5162	$127.52	$127.50	$127.50
Purchase #6	$75.93	12.676%	$85.5549	$85.55	$85.55	$85.60
Purchase #7	$229.58	13.594%	$260.7891	$260.79	$260.80	$260.80
7 purchase totals =	$840.64		$930.1023	$930.10	$930.10	$930.20