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	$228.85	12.516%	$257.4929	$257.49	$257.50	$257.50
Purchase #2	$84.73	5.714%	$89.5715	$89.57	$89.55	$89.60
Purchase #3	$128.83	6.274%	$136.9128	$136.91	$136.90	$136.90
Purchase #4	$193.94	9.450%	$212.2673	$212.27	$212.25	$212.30
Purchase #5	$20.30	9.391%	$22.2064	$22.21	$22.20	$22.20
Purchase #6	$74.88	10.576%	$82.7993	$82.80	$82.80	$82.80
Purchase #7	$228.52	4.427%	$238.6366	$238.64	$238.65	$238.60
7 purchase totals =	$960.05		$1,039.8868	$1,039.89	$1,039.85	$1,039.90