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	$188.86	5.735%	$199.6911	$199.69	$199.70	$199.70
Purchase #2	$33.77	12.500%	$37.9913	$37.99	$38.00	$38.00
Purchase #3	$53.75	10.238%	$59.2529	$59.25	$59.25	$59.30
Purchase #4	$213.92	3.665%	$221.7602	$221.76	$221.75	$221.80
Purchase #5	$45.61	10.544%	$50.4191	$50.42	$50.40	$50.40
Purchase #6	$40.56	10.511%	$44.8233	$44.82	$44.80	$44.80
Purchase #7	$21.81	13.682%	$24.794	$24.79	$24.80	$24.80
7 purchase totals =	$598.28		$638.7319	$638.72	$638.70	$638.80