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	$35.67	9.260%	$38.973	$38.97	$38.95	$39.00
Purchase #2	$12.57	6.274%	$13.3586	$13.36	$13.35	$13.40
Purchase #3	$93.90	6.719%	$100.2091	$100.21	$100.20	$100.20
Purchase #4	$162.29	6.274%	$172.4721	$172.47	$172.45	$172.50
Purchase #5	$239.46	3.689%	$248.2937	$248.29	$248.30	$248.30
Purchase #6	$177.40	7.582%	$190.8505	$190.85	$190.85	$190.90
Purchase #7	$82.93	6.481%	$88.3047	$88.30	$88.30	$88.30
7 purchase totals =	$804.22		$852.4617	$852.45	$852.40	$852.60