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	$19.94	4.115%	$20.7605	$20.76	$20.75	$20.80
Purchase #2	$30.75	3.761%	$31.9065	$31.91	$31.90	$31.90
Purchase #3	$161.83	3.328%	$167.2157	$167.22	$167.20	$167.20
Purchase #4	$102.82	10.387%	$113.4999	$113.50	$113.50	$113.50
Purchase #5	$27.88	12.833%	$31.4578	$31.46	$31.45	$31.50
Purchase #6	$79.80	8.590%	$86.6548	$86.65	$86.65	$86.70
Purchase #7	$148.80	3.142%	$153.4753	$153.48	$153.50	$153.50
7 purchase totals =	$571.82		$604.9705	$604.98	$604.95	$605.10