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	$197.97	12.421%	$222.5599	$222.56	$222.55	$222.60
Purchase #2	$221.87	12.412%	$249.4085	$249.41	$249.40	$249.40
Purchase #3	$117.73	9.461%	$128.8684	$128.87	$128.85	$128.90
Purchase #4	$236.67	13.122%	$267.7258	$267.73	$267.75	$267.70
Purchase #5	$116.43	13.298%	$131.9129	$131.91	$131.90	$131.90
Purchase #6	$150.44	12.708%	$169.5579	$169.56	$169.55	$169.60
Purchase #7	$87.78	3.172%	$90.5644	$90.56	$90.55	$90.60
7 purchase totals =	$1,128.89		$1,260.5978	$1,260.60	$1,260.55	$1,260.70