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	$129.83	10.477%	$143.4323	$143.43	$143.45	$143.40
Purchase #2	$91.48	11.158%	$101.6873	$101.69	$101.70	$101.70
Purchase #3	$84.83	5.418%	$89.4261	$89.43	$89.45	$89.40
Purchase #4	$200.86	5.447%	$211.8008	$211.80	$211.80	$211.80
Purchase #5	$101.76	9.869%	$111.8027	$111.80	$111.80	$111.80
Purchase #6	$163.40	13.369%	$185.2449	$185.24	$185.25	$185.20
Purchase #7	$27.97	12.232%	$31.3913	$31.39	$31.40	$31.40
7 purchase totals =	$800.13		$874.7854	$874.78	$874.85	$874.70