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	$91.63	13.515%	$104.0138	$104.01	$104.00	$104.00
Purchase #2	$74.86	9.399%	$81.8961	$81.90	$81.90	$81.90
Purchase #3	$79.71	8.819%	$86.7396	$86.74	$86.75	$86.70
Purchase #4	$133.38	3.323%	$137.8122	$137.81	$137.80	$137.80
Purchase #5	$40.76	10.192%	$44.9143	$44.91	$44.90	$44.90
Purchase #6	$231.86	6.724%	$247.4503	$247.45	$247.45	$247.50
Purchase #7	$248.46	10.822%	$275.3483	$275.35	$275.35	$275.30
7 purchase totals =	$900.66		$978.1746	$978.17	$978.15	$978.10