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	$80.71	10.772%	$89.4041	$89.40	$89.40	$89.40
Purchase #2	$141.40	13.620%	$160.6587	$160.66	$160.65	$160.70
Purchase #3	$139.82	3.469%	$144.6704	$144.67	$144.65	$144.70
Purchase #4	$164.65	5.214%	$173.2349	$173.23	$173.25	$173.20
Purchase #5	$70.48	11.425%	$78.5323	$78.53	$78.55	$78.50
Purchase #6	$209.87	6.483%	$223.4759	$223.48	$223.50	$223.50
Purchase #7	$113.63	13.714%	$129.2132	$129.21	$129.20	$129.20
7 purchase totals =	$920.56		$999.1895	$999.18	$999.20	$999.20