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	$171.97	5.215%	$180.9382	$180.94	$180.95	$180.90
Purchase #2	$7.56	13.867%	$8.6083	$8.61	$8.60	$8.60
Purchase #3	$54.27	11.215%	$60.3564	$60.36	$60.35	$60.40
Purchase #4	$136.78	4.756%	$143.2853	$143.29	$143.30	$143.30
Purchase #5	$176.98	10.110%	$194.8727	$194.87	$194.85	$194.90
Purchase #6	$13.67	13.762%	$15.5513	$15.55	$15.55	$15.60
Purchase #7	$56.42	9.678%	$61.8803	$61.88	$61.90	$61.90
7 purchase totals =	$617.65		$665.4925	$665.50	$665.50	$665.60