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	$92.79	7.623%	$99.8634	$99.86	$99.85	$99.90
Purchase #2	$245.39	3.440%	$253.8314	$253.83	$253.85	$253.80
Purchase #3	$100.65	12.731%	$113.4638	$113.46	$113.45	$113.50
Purchase #4	$115.51	5.172%	$121.4842	$121.48	$121.50	$121.50
Purchase #5	$203.77	13.556%	$231.3931	$231.39	$231.40	$231.40
Purchase #6	$53.29	11.256%	$59.2883	$59.29	$59.30	$59.30
Purchase #7	$26.70	10.176%	$29.417	$29.42	$29.40	$29.40
7 purchase totals =	$838.10		$908.7412	$908.73	$908.75	$908.80