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	$52.45	12.757%	$59.141	$59.14	$59.15	$59.10
Purchase #2	$130.46	7.651%	$140.4415	$140.44	$140.45	$140.40
Purchase #3	$28.62	11.675%	$31.9614	$31.96	$31.95	$32.00
Purchase #4	$166.80	10.595%	$184.4725	$184.47	$184.45	$184.50
Purchase #5	$19.78	9.511%	$21.6613	$21.66	$21.65	$21.70
Purchase #6	$60.27	11.869%	$67.4234	$67.42	$67.40	$67.40
Purchase #7	$104.76	10.659%	$115.9264	$115.93	$115.95	$115.90
7 purchase totals =	$563.14		$621.0275	$621.02	$621.00	$621.00