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	$18.36	11.437%	$20.4598	$20.46	$20.45	$20.50
Purchase #2	$15.39	12.207%	$17.2687	$17.27	$17.25	$17.30
Purchase #3	$169.67	12.835%	$191.4471	$191.45	$191.45	$191.40
Purchase #4	$156.76	11.303%	$174.4786	$174.48	$174.50	$174.50
Purchase #5	$72.43	11.391%	$80.6805	$80.68	$80.70	$80.70
Purchase #6	$107.69	5.333%	$113.4331	$113.43	$113.45	$113.40
Purchase #7	$38.79	10.328%	$42.7962	$42.80	$42.80	$42.80
7 purchase totals =	$579.09		$640.5640	$640.57	$640.60	$640.60