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	$45.98	7.584%	$49.4671	$49.47	$49.45	$49.50
Purchase #2	$27.81	4.481%	$29.0562	$29.06	$29.05	$29.10
Purchase #3	$79.59	3.654%	$82.4982	$82.50	$82.50	$82.50
Purchase #4	$207.33	5.335%	$218.3911	$218.39	$218.40	$218.40
Purchase #5	$77.41	5.812%	$81.9091	$81.91	$81.90	$81.90
Purchase #6	$154.75	10.870%	$171.5713	$171.57	$171.55	$171.60
Purchase #7	$22.85	12.310%	$25.6628	$25.66	$25.65	$25.70
7 purchase totals =	$615.72		$658.5558	$658.56	$658.50	$658.70