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	$35.51	10.506%	$39.2407	$39.24	$39.25	$39.20
Purchase #2	$27.84	11.602%	$31.07	$31.07	$31.05	$31.10
Purchase #3	$250.32	9.361%	$273.7525	$273.75	$273.75	$273.80
Purchase #4	$70.75	3.610%	$73.3041	$73.30	$73.30	$73.30
Purchase #5	$50.44	11.476%	$56.2285	$56.23	$56.25	$56.20
Purchase #6	$38.97	11.332%	$43.3861	$43.39	$43.40	$43.40
Purchase #7	$46.32	13.511%	$52.5783	$52.58	$52.60	$52.60
7 purchase totals =	$520.15		$569.5602	$569.56	$569.60	$569.60