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	$166.64	8.178%	$180.2678	$180.27	$180.25	$180.30
Purchase #2	$165.45	6.440%	$176.105	$176.11	$176.10	$176.10
Purchase #3	$98.64	5.287%	$103.8551	$103.86	$103.85	$103.90
Purchase #4	$74.79	7.134%	$80.1255	$80.13	$80.15	$80.10
Purchase #5	$124.66	9.857%	$136.9477	$136.95	$136.95	$136.90
Purchase #6	$164.38	12.441%	$184.8305	$184.83	$184.85	$184.80
Purchase #7	$126.75	11.723%	$141.6089	$141.61	$141.60	$141.60
7 purchase totals =	$921.31		$1,003.7405	$1,003.76	$1,003.75	$1,003.70