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	$155.47	9.311%	$169.9458	$169.95	$169.95	$169.90
Purchase #2	$121.83	4.701%	$127.5572	$127.56	$127.55	$127.60
Purchase #3	$112.89	12.676%	$127.1999	$127.20	$127.20	$127.20
Purchase #4	$249.44	12.368%	$280.2907	$280.29	$280.30	$280.30
Purchase #5	$19.86	6.364%	$21.1239	$21.12	$21.10	$21.10
Purchase #6	$10.36	4.779%	$10.8551	$10.86	$10.85	$10.90
Purchase #7	$184.98	4.453%	$193.2172	$193.22	$193.20	$193.20
7 purchase totals =	$854.83		$930.1898	$930.20	$930.15	$930.20