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	$245.78	12.535%	$276.5885	$276.59	$276.60	$276.60
Purchase #2	$245.30	3.475%	$253.8242	$253.82	$253.80	$253.80
Purchase #3	$231.68	9.641%	$254.0163	$254.02	$254.00	$254.00
Purchase #4	$118.94	4.653%	$124.4743	$124.47	$124.45	$124.50
Purchase #5	$122.54	3.417%	$126.7272	$126.73	$126.75	$126.70
Purchase #6	$35.78	12.712%	$40.3284	$40.33	$40.35	$40.30
Purchase #7	$42.69	12.185%	$47.8918	$47.89	$47.90	$47.90
7 purchase totals =	$1,042.71		$1,123.8507	$1,123.85	$1,123.85	$1,123.80