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	$249.44	13.697%	$283.6058	$283.61	$283.60	$283.60
Purchase #2	$218.48	10.141%	$240.6361	$240.64	$240.65	$240.60
Purchase #3	$36.98	10.590%	$40.8962	$40.90	$40.90	$40.90
Purchase #4	$240.79	10.399%	$265.8298	$265.83	$265.85	$265.80
Purchase #5	$100.27	5.584%	$105.8691	$105.87	$105.85	$105.90
Purchase #6	$175.30	5.684%	$185.2641	$185.26	$185.25	$185.30
Purchase #7	$135.46	13.459%	$153.6916	$153.69	$153.70	$153.70
7 purchase totals =	$1,156.72		$1,275.7927	$1,275.80	$1,275.80	$1,275.80