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	$167.41	11.240%	$186.2269	$186.23	$186.25	$186.20
Purchase #2	$242.38	3.409%	$250.6427	$250.64	$250.65	$250.60
Purchase #3	$104.61	4.774%	$109.6041	$109.60	$109.60	$109.60
Purchase #4	$230.33	6.463%	$245.2162	$245.22	$245.20	$245.20
Purchase #5	$146.93	3.134%	$151.5348	$151.53	$151.55	$151.50
Purchase #6	$154.51	12.141%	$173.2691	$173.27	$173.25	$173.30
Purchase #7	$67.92	12.483%	$76.3985	$76.40	$76.40	$76.40
7 purchase totals =	$1,114.09		$1,192.8923	$1,192.89	$1,192.90	$1,192.80