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	$38.30	4.473%	$40.0132	$40.01	$40.00	$40.00
Purchase #2	$31.40	11.591%	$35.0396	$35.04	$35.05	$35.00
Purchase #3	$208.49	3.143%	$215.0428	$215.04	$215.05	$215.00
Purchase #4	$173.35	13.422%	$196.617	$196.62	$196.60	$196.60
Purchase #5	$224.40	6.141%	$238.1804	$238.18	$238.20	$238.20
Purchase #6	$38.84	12.222%	$43.587	$43.59	$43.60	$43.60
Purchase #7	$196.77	13.751%	$223.8278	$223.83	$223.85	$223.80
7 purchase totals =	$911.55		$992.3078	$992.31	$992.35	$992.20