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	$35.81	8.142%	$38.7257	$38.73	$38.75	$38.70
Purchase #2	$33.80	8.639%	$36.72	$36.72	$36.70	$36.70
Purchase #3	$216.90	11.298%	$241.4054	$241.41	$241.40	$241.40
Purchase #4	$66.77	7.234%	$71.6001	$71.60	$71.60	$71.60
Purchase #5	$41.67	9.396%	$45.5853	$45.59	$45.60	$45.60
Purchase #6	$152.30	9.824%	$167.262	$167.26	$167.25	$167.30
Purchase #7	$77.92	4.356%	$81.3142	$81.31	$81.30	$81.30
7 purchase totals =	$625.17		$682.6127	$682.62	$682.60	$682.60