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	$170.68	11.157%	$189.7228	$189.72	$189.70	$189.70
Purchase #2	$105.83	3.215%	$109.2324	$109.23	$109.25	$109.20
Purchase #3	$224.62	6.830%	$239.9615	$239.96	$239.95	$240.00
Purchase #4	$121.53	10.145%	$133.8592	$133.86	$133.85	$133.90
Purchase #5	$133.69	13.296%	$151.4654	$151.47	$151.45	$151.50
Purchase #6	$152.37	9.825%	$167.3404	$167.34	$167.35	$167.30
Purchase #7	$209.41	4.256%	$218.3225	$218.32	$218.30	$218.30
7 purchase totals =	$1,118.13		$1,209.9042	$1,209.90	$1,209.85	$1,209.90