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	$39.94	5.396%	$42.0952	$42.10	$42.10	$42.10
Purchase #2	$114.91	3.358%	$118.7687	$118.77	$118.75	$118.80
Purchase #3	$182.25	4.114%	$189.7478	$189.75	$189.75	$189.70
Purchase #4	$41.72	7.714%	$44.9383	$44.94	$44.95	$44.90
Purchase #5	$29.98	5.597%	$31.658	$31.66	$31.65	$31.70
Purchase #6	$114.39	11.624%	$127.6867	$127.69	$127.70	$127.70
Purchase #7	$178.58	4.133%	$185.9607	$185.96	$185.95	$186.00
7 purchase totals =	$701.77		$740.8554	$740.87	$740.85	$740.90