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	$155.27	12.615%	$174.8573	$174.86	$174.85	$174.90
Purchase #2	$140.31	9.187%	$153.2003	$153.20	$153.20	$153.20
Purchase #3	$222.29	4.148%	$231.5106	$231.51	$231.50	$231.50
Purchase #4	$236.43	9.114%	$257.9782	$257.98	$258.00	$258.00
Purchase #5	$85.61	8.459%	$92.8517	$92.85	$92.85	$92.90
Purchase #6	$214.59	3.821%	$222.7895	$222.79	$222.80	$222.80
Purchase #7	$85.62	4.570%	$89.5328	$89.53	$89.55	$89.50
7 purchase totals =	$1,140.12		$1,222.7204	$1,222.72	$1,222.75	$1,222.80