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	$84.92	7.224%	$91.0546	$91.05	$91.05	$91.10
Purchase #2	$232.34	12.602%	$261.6195	$261.62	$261.60	$261.60
Purchase #3	$26.79	9.438%	$29.3184	$29.32	$29.30	$29.30
Purchase #4	$31.32	10.863%	$34.7223	$34.72	$34.70	$34.70
Purchase #5	$161.85	9.644%	$177.4588	$177.46	$177.45	$177.50
Purchase #6	$233.86	9.424%	$255.899	$255.90	$255.90	$255.90
Purchase #7	$127.46	3.139%	$131.461	$131.46	$131.45	$131.50
7 purchase totals =	$898.54		$981.5336	$981.53	$981.45	$981.60