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	$114.57	5.219%	$120.5494	$120.55	$120.55	$120.50
Purchase #2	$57.81	3.170%	$59.6426	$59.64	$59.65	$59.60
Purchase #3	$89.35	11.340%	$99.4823	$99.48	$99.50	$99.50
Purchase #4	$97.41	7.259%	$104.481	$104.48	$104.50	$104.50
Purchase #5	$154.31	5.492%	$162.7847	$162.78	$162.80	$162.80
Purchase #6	$152.63	5.504%	$161.0308	$161.03	$161.05	$161.00
Purchase #7	$152.69	6.798%	$163.0699	$163.07	$163.05	$163.10
7 purchase totals =	$818.77		$871.0407	$871.03	$871.10	$871.00