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	$116.71	11.741%	$130.4129	$130.41	$130.40	$130.40
Purchase #2	$116.51	6.874%	$124.5189	$124.52	$124.50	$124.50
Purchase #3	$186.83	9.648%	$204.8554	$204.86	$204.85	$204.90
Purchase #4	$42.74	3.304%	$44.1521	$44.15	$44.15	$44.20
Purchase #5	$195.99	13.547%	$222.5408	$222.54	$222.55	$222.50
Purchase #6	$127.55	11.706%	$142.481	$142.48	$142.50	$142.50
Purchase #7	$50.45	5.188%	$53.0673	$53.07	$53.05	$53.10
7 purchase totals =	$836.78		$922.0284	$922.03	$922.00	$922.10