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	$172.76	9.458%	$189.0996	$189.10	$189.10	$189.10
Purchase #2	$179.30	13.783%	$204.0129	$204.01	$204.00	$204.00
Purchase #3	$39.76	7.626%	$42.7921	$42.79	$42.80	$42.80
Purchase #4	$142.47	7.259%	$152.8119	$152.81	$152.80	$152.80
Purchase #5	$75.68	10.246%	$83.4342	$83.43	$83.45	$83.40
Purchase #6	$128.65	10.650%	$142.3512	$142.35	$142.35	$142.40
Purchase #7	$52.56	12.704%	$59.2372	$59.24	$59.25	$59.20
7 purchase totals =	$791.18		$873.7391	$873.73	$873.75	$873.70