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	$28.54	10.738%	$31.6046	$31.60	$31.60	$31.60
Purchase #2	$178.95	6.323%	$190.265	$190.27	$190.25	$190.30
Purchase #3	$192.99	3.692%	$200.1152	$200.12	$200.10	$200.10
Purchase #4	$33.37	5.253%	$35.1229	$35.12	$35.10	$35.10
Purchase #5	$184.73	5.280%	$194.4837	$194.48	$194.50	$194.50
Purchase #6	$68.61	3.495%	$71.0079	$71.01	$71.00	$71.00
Purchase #7	$122.95	13.764%	$139.8728	$139.87	$139.85	$139.90
7 purchase totals =	$810.14		$862.4721	$862.47	$862.40	$862.50