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	$49.40	13.171%	$55.9065	$55.91	$55.90	$55.90
Purchase #2	$99.89	5.621%	$105.5048	$105.50	$105.50	$105.50
Purchase #3	$145.35	11.825%	$162.5376	$162.54	$162.55	$162.50
Purchase #4	$125.88	6.528%	$134.0974	$134.10	$134.10	$134.10
Purchase #5	$40.33	3.455%	$41.7234	$41.72	$41.70	$41.70
Purchase #6	$179.38	9.134%	$195.7646	$195.76	$195.75	$195.80
Purchase #7	$50.75	12.582%	$57.1354	$57.14	$57.15	$57.10
7 purchase totals =	$690.98		$752.6697	$752.67	$752.65	$752.60