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	$49.96	10.170%	$55.0409	$55.04	$55.05	$55.00
Purchase #2	$249.69	12.228%	$280.2221	$280.22	$280.20	$280.20
Purchase #3	$79.62	13.181%	$90.1147	$90.11	$90.10	$90.10
Purchase #4	$79.98	12.568%	$90.0319	$90.03	$90.05	$90.00
Purchase #5	$195.66	12.651%	$220.4129	$220.41	$220.40	$220.40
Purchase #6	$27.42	8.156%	$29.6564	$29.66	$29.65	$29.70
Purchase #7	$150.43	9.178%	$164.2365	$164.24	$164.25	$164.20
7 purchase totals =	$832.76		$929.7154	$929.71	$929.70	$929.60