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	$31.54	13.822%	$35.8995	$35.90	$35.90	$35.90
Purchase #2	$30.30	7.617%	$32.608	$32.61	$32.60	$32.60
Purchase #3	$131.85	3.203%	$136.0732	$136.07	$136.05	$136.10
Purchase #4	$230.25	4.252%	$240.0402	$240.04	$240.05	$240.00
Purchase #5	$197.34	12.129%	$221.2754	$221.28	$221.30	$221.30
Purchase #6	$106.76	6.658%	$113.8681	$113.87	$113.85	$113.90
Purchase #7	$41.27	5.511%	$43.5444	$43.54	$43.55	$43.50
7 purchase totals =	$769.31		$823.3088	$823.31	$823.30	$823.30