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	$185.88	6.165%	$197.3395	$197.34	$197.35	$197.30
Purchase #2	$150.27	6.687%	$160.3186	$160.32	$160.30	$160.30
Purchase #3	$47.72	7.305%	$51.2059	$51.21	$51.20	$51.20
Purchase #4	$102.67	9.258%	$112.1752	$112.18	$112.20	$112.20
Purchase #5	$52.85	5.786%	$55.9079	$55.91	$55.90	$55.90
Purchase #6	$82.50	8.687%	$89.6668	$89.67	$89.65	$89.70
Purchase #7	$211.67	12.622%	$238.387	$238.39	$238.40	$238.40
7 purchase totals =	$833.56		$905.0009	$905.02	$905.00	$905.00