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	$50.52	5.116%	$53.1046	$53.10	$53.10	$53.10
Purchase #2	$208.51	11.138%	$231.7338	$231.73	$231.75	$231.70
Purchase #3	$239.45	7.272%	$256.8628	$256.86	$256.85	$256.90
Purchase #4	$45.48	11.423%	$50.6752	$50.68	$50.70	$50.70
Purchase #5	$27.26	7.401%	$29.2775	$29.28	$29.30	$29.30
Purchase #6	$54.54	9.254%	$59.5871	$59.59	$59.60	$59.60
Purchase #7	$189.74	4.494%	$198.2669	$198.27	$198.25	$198.30
7 purchase totals =	$815.50		$879.5079	$879.51	$879.55	$879.60