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	$50.85	13.113%	$57.518	$57.52	$57.50	$57.50
Purchase #2	$245.61	7.822%	$264.8216	$264.82	$264.80	$264.80
Purchase #3	$32.56	10.652%	$36.0283	$36.03	$36.05	$36.00
Purchase #4	$46.68	8.110%	$50.4657	$50.47	$50.45	$50.50
Purchase #5	$123.27	4.680%	$129.039	$129.04	$129.05	$129.00
Purchase #6	$92.45	12.303%	$103.8241	$103.82	$103.80	$103.80
Purchase #7	$197.75	12.311%	$222.095	$222.10	$222.10	$222.10
7 purchase totals =	$789.17		$863.7917	$863.80	$863.75	$863.70