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	$198.72	4.183%	$207.0325	$207.03	$207.05	$207.00
Purchase #2	$65.57	10.483%	$72.4437	$72.44	$72.45	$72.40
Purchase #3	$86.65	13.117%	$98.0159	$98.02	$98.00	$98.00
Purchase #4	$85.67	5.574%	$90.4452	$90.45	$90.45	$90.40
Purchase #5	$104.35	13.313%	$118.2421	$118.24	$118.25	$118.20
Purchase #6	$55.39	10.550%	$61.2336	$61.23	$61.25	$61.20
Purchase #7	$33.74	6.478%	$35.9257	$35.93	$35.95	$35.90
7 purchase totals =	$630.09		$683.3387	$683.34	$683.40	$683.10