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	$172.57	3.797%	$179.1225	$179.12	$179.10	$179.10
Purchase #2	$106.32	6.455%	$113.183	$113.18	$113.20	$113.20
Purchase #3	$69.90	4.185%	$72.8253	$72.83	$72.85	$72.80
Purchase #4	$5.32	11.403%	$5.9266	$5.93	$5.95	$5.90
Purchase #5	$202.56	10.317%	$223.4581	$223.46	$223.45	$223.50
Purchase #6	$203.60	12.867%	$229.7972	$229.80	$229.80	$229.80
Purchase #7	$179.29	6.407%	$190.7771	$190.78	$190.80	$190.80
7 purchase totals =	$939.56		$1,015.0898	$1,015.10	$1,015.15	$1,015.10