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	$94.82	13.341%	$107.4699	$107.47	$107.45	$107.50
Purchase #2	$235.64	13.545%	$267.5574	$267.56	$267.55	$267.60
Purchase #3	$232.25	5.755%	$245.616	$245.62	$245.60	$245.60
Purchase #4	$165.65	12.211%	$185.8775	$185.88	$185.90	$185.90
Purchase #5	$118.73	6.618%	$126.5876	$126.59	$126.60	$126.60
Purchase #6	$58.93	8.652%	$64.0286	$64.03	$64.05	$64.00
Purchase #7	$133.76	12.374%	$150.3115	$150.31	$150.30	$150.30
7 purchase totals =	$1,039.78		$1,147.4485	$1,147.46	$1,147.45	$1,147.50