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	$111.36	11.242%	$123.8791	$123.88	$123.90	$123.90
Purchase #2	$229.46	12.353%	$257.8052	$257.81	$257.80	$257.80
Purchase #3	$40.72	7.623%	$43.8241	$43.82	$43.80	$43.80
Purchase #4	$65.90	10.689%	$72.9441	$72.94	$72.95	$72.90
Purchase #5	$30.61	3.642%	$31.7248	$31.72	$31.70	$31.70
Purchase #6	$193.28	12.146%	$216.7558	$216.76	$216.75	$216.80
Purchase #7	$33.57	10.403%	$37.0623	$37.06	$37.05	$37.10
7 purchase totals =	$704.90		$783.9954	$783.99	$783.95	$784.00