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	$29.80	6.813%	$31.8303	$31.83	$31.85	$31.80
Purchase #2	$244.50	4.630%	$255.8204	$255.82	$255.80	$255.80
Purchase #3	$56.46	9.383%	$61.7576	$61.76	$61.75	$61.80
Purchase #4	$193.81	6.180%	$205.7875	$205.79	$205.80	$205.80
Purchase #5	$82.97	10.796%	$91.9274	$91.93	$91.95	$91.90
Purchase #6	$30.55	9.717%	$33.5185	$33.52	$33.50	$33.50
Purchase #7	$242.43	7.850%	$261.4608	$261.46	$261.45	$261.50
7 purchase totals =	$880.52		$942.1025	$942.11	$942.10	$942.10