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	$80.60	12.132%	$90.3784	$90.38	$90.40	$90.40
Purchase #2	$50.58	9.218%	$55.2425	$55.24	$55.25	$55.20
Purchase #3	$39.85	5.151%	$41.9027	$41.90	$41.90	$41.90
Purchase #4	$69.50	3.392%	$71.8574	$71.86	$71.85	$71.90
Purchase #5	$228.65	4.132%	$238.0978	$238.10	$238.10	$238.10
Purchase #6	$154.67	11.543%	$172.5236	$172.52	$172.50	$172.50
Purchase #7	$196.58	13.801%	$223.71	$223.71	$223.70	$223.70
7 purchase totals =	$820.43		$893.7124	$893.71	$893.70	$893.70