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	$209.53	7.359%	$224.9493	$224.95	$224.95	$224.90
Purchase #2	$109.84	4.744%	$115.0508	$115.05	$115.05	$115.10
Purchase #3	$52.50	9.137%	$57.2969	$57.30	$57.30	$57.30
Purchase #4	$173.50	13.149%	$196.3135	$196.31	$196.30	$196.30
Purchase #5	$77.69	5.143%	$81.6856	$81.69	$81.70	$81.70
Purchase #6	$158.76	6.320%	$168.7936	$168.79	$168.80	$168.80
Purchase #7	$53.90	3.380%	$55.7218	$55.72	$55.70	$55.70
7 purchase totals =	$835.72		$899.8115	$899.81	$899.80	$899.80