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	$20.76	3.119%	$21.4075	$21.41	$21.40	$21.40
Purchase #2	$194.88	7.318%	$209.1413	$209.14	$209.15	$209.10
Purchase #3	$115.66	4.373%	$120.7178	$120.72	$120.70	$120.70
Purchase #4	$152.56	9.197%	$166.5909	$166.59	$166.60	$166.60
Purchase #5	$17.97	3.373%	$18.5761	$18.58	$18.60	$18.60
Purchase #6	$39.62	6.159%	$42.0602	$42.06	$42.05	$42.10
Purchase #7	$122.48	4.562%	$128.0675	$128.07	$128.05	$128.10
7 purchase totals =	$663.93		$706.5613	$706.57	$706.55	$706.60