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	$138.75	11.156%	$154.229	$154.23	$154.25	$154.20
Purchase #2	$32.64	7.330%	$35.0325	$35.03	$35.05	$35.00
Purchase #3	$38.61	13.799%	$43.9378	$43.94	$43.95	$43.90
Purchase #4	$75.39	11.180%	$83.8186	$83.82	$83.80	$83.80
Purchase #5	$43.87	4.292%	$45.7529	$45.75	$45.75	$45.80
Purchase #6	$239.35	6.747%	$255.4989	$255.50	$255.50	$255.50
Purchase #7	$155.30	4.811%	$162.7715	$162.77	$162.75	$162.80
7 purchase totals =	$723.91		$781.0412	$781.04	$781.05	$781.00