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	$33.48	11.775%	$37.4223	$37.42	$37.40	$37.40
Purchase #2	$34.78	12.140%	$39.0023	$39.00	$39.00	$39.00
Purchase #3	$80.40	11.401%	$89.5664	$89.57	$89.55	$89.60
Purchase #4	$35.30	9.759%	$38.7449	$38.74	$38.75	$38.70
Purchase #5	$195.80	12.507%	$220.2887	$220.29	$220.30	$220.30
Purchase #6	$32.71	6.335%	$34.7822	$34.78	$34.80	$34.80
Purchase #7	$233.35	7.691%	$251.2969	$251.30	$251.30	$251.30
7 purchase totals =	$645.82		$711.1037	$711.10	$711.10	$711.10