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	$100.40	6.476%	$106.9019	$106.90	$106.90	$106.90
Purchase #2	$22.35	6.600%	$23.8251	$23.83	$23.85	$23.80
Purchase #3	$156.55	7.817%	$168.7875	$168.79	$168.80	$168.80
Purchase #4	$37.48	13.799%	$42.6519	$42.65	$42.65	$42.70
Purchase #5	$42.30	12.200%	$47.4606	$47.46	$47.45	$47.50
Purchase #6	$171.97	5.285%	$181.0586	$181.06	$181.05	$181.10
Purchase #7	$86.89	10.445%	$95.9657	$95.97	$95.95	$96.00
7 purchase totals =	$617.94		$666.6513	$666.66	$666.65	$666.80