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	$238.47	4.248%	$248.6002	$248.60	$248.60	$248.60
Purchase #2	$158.44	7.731%	$170.689	$170.69	$170.70	$170.70
Purchase #3	$130.34	9.622%	$142.8813	$142.88	$142.90	$142.90
Purchase #4	$73.34	12.656%	$82.6219	$82.62	$82.60	$82.60
Purchase #5	$36.83	9.573%	$40.3557	$40.36	$40.35	$40.40
Purchase #6	$169.35	13.337%	$191.9362	$191.94	$191.95	$191.90
Purchase #7	$56.45	9.483%	$61.8032	$61.80	$61.80	$61.80
7 purchase totals =	$863.22		$938.8875	$938.89	$938.90	$938.90