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	$89.45	7.555%	$96.2079	$96.21	$96.20	$96.20
Purchase #2	$40.53	12.302%	$45.516	$45.52	$45.50	$45.50
Purchase #3	$143.28	5.633%	$151.351	$151.35	$151.35	$151.40
Purchase #4	$71.74	12.751%	$80.8876	$80.89	$80.90	$80.90
Purchase #5	$213.48	11.598%	$238.2394	$238.24	$238.25	$238.20
Purchase #6	$30.37	10.610%	$33.5923	$33.59	$33.60	$33.60
Purchase #7	$21.35	11.872%	$23.8847	$23.88	$23.90	$23.90
7 purchase totals =	$610.20		$669.6789	$669.68	$669.70	$669.70