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	$35.61	5.241%	$37.4763	$37.48	$37.50	$37.50
Purchase #2	$135.32	13.252%	$153.2526	$153.25	$153.25	$153.30
Purchase #3	$53.95	4.155%	$56.1916	$56.19	$56.20	$56.20
Purchase #4	$110.53	11.419%	$123.1514	$123.15	$123.15	$123.20
Purchase #5	$54.76	12.575%	$61.6461	$61.65	$61.65	$61.60
Purchase #6	$126.81	13.312%	$143.6909	$143.69	$143.70	$143.70
Purchase #7	$23.89	5.236%	$25.1409	$25.14	$25.15	$25.10
7 purchase totals =	$540.87		$600.5498	$600.55	$600.60	$600.60