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	$30.28	10.590%	$33.4867	$33.49	$33.50	$33.50
Purchase #2	$245.94	12.830%	$277.4941	$277.49	$277.50	$277.50
Purchase #3	$85.39	11.404%	$95.1279	$95.13	$95.15	$95.10
Purchase #4	$85.49	9.794%	$93.8629	$93.86	$93.85	$93.90
Purchase #5	$51.45	10.128%	$56.6609	$56.66	$56.65	$56.70
Purchase #6	$78.46	9.383%	$85.8219	$85.82	$85.80	$85.80
Purchase #7	$169.69	12.292%	$190.5483	$190.55	$190.55	$190.50
7 purchase totals =	$746.70		$833.0027	$833.00	$833.00	$833.00