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	$119.47	3.280%	$123.3886	$123.39	$123.40	$123.40
Purchase #2	$18.87	6.845%	$20.1617	$20.16	$20.15	$20.20
Purchase #3	$94.57	9.635%	$103.6818	$103.68	$103.70	$103.70
Purchase #4	$124.65	7.382%	$133.8517	$133.85	$133.85	$133.90
Purchase #5	$95.70	8.154%	$103.5034	$103.50	$103.50	$103.50
Purchase #6	$88.27	9.234%	$96.4209	$96.42	$96.40	$96.40
Purchase #7	$81.63	7.851%	$88.0388	$88.04	$88.05	$88.00
7 purchase totals =	$623.16		$669.0469	$669.04	$669.05	$669.10