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	$75.84	3.778%	$78.7052	$78.71	$78.70	$78.70
Purchase #2	$95.59	5.504%	$100.8513	$100.85	$100.85	$100.90
Purchase #3	$177.96	10.221%	$196.1493	$196.15	$196.15	$196.10
Purchase #4	$231.26	6.162%	$245.5102	$245.51	$245.50	$245.50
Purchase #5	$26.27	11.647%	$29.3297	$29.33	$29.35	$29.30
Purchase #6	$31.57	3.349%	$32.6273	$32.63	$32.65	$32.60
Purchase #7	$188.45	4.427%	$196.7927	$196.79	$196.80	$196.80
7 purchase totals =	$826.94		$879.9657	$879.97	$880.00	$879.90