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	$37.98	11.692%	$42.4206	$42.42	$42.40	$42.40
Purchase #2	$196.60	10.392%	$217.0307	$217.03	$217.05	$217.00
Purchase #3	$173.65	6.260%	$184.5205	$184.52	$184.50	$184.50
Purchase #4	$29.40	4.185%	$30.6304	$30.63	$30.65	$30.60
Purchase #5	$98.29	4.378%	$102.5931	$102.59	$102.60	$102.60
Purchase #6	$156.79	7.315%	$168.2592	$168.26	$168.25	$168.30
Purchase #7	$239.61	11.247%	$266.5589	$266.56	$266.55	$266.60
7 purchase totals =	$932.32		$1,012.0134	$1,012.01	$1,012.00	$1,012.00