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	$137.31	6.796%	$146.6416	$146.64	$146.65	$146.60
Purchase #2	$221.26	13.234%	$250.5415	$250.54	$250.55	$250.50
Purchase #3	$38.41	10.468%	$42.4308	$42.43	$42.45	$42.40
Purchase #4	$189.29	8.860%	$206.0611	$206.06	$206.05	$206.10
Purchase #5	$107.76	4.664%	$112.7859	$112.79	$112.80	$112.80
Purchase #6	$188.86	7.623%	$203.2568	$203.26	$203.25	$203.30
Purchase #7	$37.52	12.602%	$42.2483	$42.25	$42.25	$42.20
7 purchase totals =	$920.41		$1,003.9660	$1,003.97	$1,004.00	$1,003.90