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	$240.30	6.755%	$256.5323	$256.53	$256.55	$256.50
Purchase #2	$185.89	12.800%	$209.6839	$209.68	$209.70	$209.70
Purchase #3	$137.78	3.409%	$142.4769	$142.48	$142.50	$142.50
Purchase #4	$51.30	12.736%	$57.8336	$57.83	$57.85	$57.80
Purchase #5	$93.57	3.149%	$96.5165	$96.52	$96.50	$96.50
Purchase #6	$244.75	5.226%	$257.5406	$257.54	$257.55	$257.50
Purchase #7	$213.34	9.132%	$232.8222	$232.82	$232.80	$232.80
7 purchase totals =	$1,166.93		$1,253.4060	$1,253.40	$1,253.45	$1,253.30