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	$60.95	8.648%	$66.221	$66.22	$66.20	$66.20
Purchase #2	$213.79	9.600%	$234.3138	$234.31	$234.30	$234.30
Purchase #3	$39.70	9.194%	$43.35	$43.35	$43.35	$43.40
Purchase #4	$218.34	9.335%	$238.722	$238.72	$238.70	$238.70
Purchase #5	$119.41	6.779%	$127.5048	$127.50	$127.50	$127.50
Purchase #6	$146.45	8.535%	$158.9495	$158.95	$158.95	$158.90
Purchase #7	$31.82	12.506%	$35.7994	$35.80	$35.80	$35.80
7 purchase totals =	$830.46		$904.8605	$904.85	$904.80	$904.80