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	$136.99	3.605%	$141.9285	$141.93	$141.95	$141.90
Purchase #2	$51.66	11.736%	$57.7228	$57.72	$57.70	$57.70
Purchase #3	$55.98	11.429%	$62.378	$62.38	$62.40	$62.40
Purchase #4	$55.60	12.485%	$62.5417	$62.54	$62.55	$62.50
Purchase #5	$32.57	10.168%	$35.8817	$35.88	$35.90	$35.90
Purchase #6	$214.60	12.227%	$240.8391	$240.84	$240.85	$240.80
Purchase #7	$159.92	11.658%	$178.5635	$178.56	$178.55	$178.60
7 purchase totals =	$707.32		$779.8553	$779.85	$779.90	$779.80