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	$50.63	8.676%	$55.0227	$55.02	$55.00	$55.00
Purchase #2	$202.68	9.832%	$222.6075	$222.61	$222.60	$222.60
Purchase #3	$190.85	4.164%	$198.797	$198.80	$198.80	$198.80
Purchase #4	$202.39	11.379%	$225.42	$225.42	$225.40	$225.40
Purchase #5	$35.98	4.269%	$37.516	$37.52	$37.50	$37.50
Purchase #6	$190.32	7.507%	$204.6073	$204.61	$204.60	$204.60
Purchase #7	$53.83	4.569%	$56.2895	$56.29	$56.30	$56.30
7 purchase totals =	$926.68		$1,000.2600	$1,000.27	$1,000.20	$1,000.20