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	$37.77	9.538%	$41.3725	$41.37	$41.35	$41.40
Purchase #2	$77.28	6.599%	$82.3797	$82.38	$82.40	$82.40
Purchase #3	$130.78	10.130%	$144.028	$144.03	$144.05	$144.00
Purchase #4	$139.77	11.471%	$155.803	$155.80	$155.80	$155.80
Purchase #5	$155.31	4.623%	$162.49	$162.49	$162.50	$162.50
Purchase #6	$239.60	11.564%	$267.3073	$267.31	$267.30	$267.30
Purchase #7	$136.86	3.148%	$141.1684	$141.17	$141.15	$141.20
7 purchase totals =	$917.37		$994.5489	$994.55	$994.55	$994.60