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	$204.71	12.159%	$229.6007	$229.60	$229.60	$229.60
Purchase #2	$87.95	4.163%	$91.6114	$91.61	$91.60	$91.60
Purchase #3	$189.45	5.207%	$199.3147	$199.31	$199.30	$199.30
Purchase #4	$49.92	9.564%	$54.6943	$54.69	$54.70	$54.70
Purchase #5	$52.37	6.577%	$55.8144	$55.81	$55.80	$55.80
Purchase #6	$144.61	8.194%	$156.4593	$156.46	$156.45	$156.50
Purchase #7	$67.90	5.212%	$71.4389	$71.44	$71.45	$71.40
7 purchase totals =	$796.91		$858.9337	$858.92	$858.90	$858.90