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	$248.72	3.738%	$258.0172	$258.02	$258.00	$258.00
Purchase #2	$150.56	10.205%	$165.9246	$165.92	$165.90	$165.90
Purchase #3	$139.96	3.311%	$144.5941	$144.59	$144.60	$144.60
Purchase #4	$182.53	8.800%	$198.5926	$198.59	$198.60	$198.60
Purchase #5	$222.52	5.319%	$234.3558	$234.36	$234.35	$234.40
Purchase #6	$240.98	12.292%	$270.6013	$270.60	$270.60	$270.60
Purchase #7	$128.76	13.310%	$145.898	$145.90	$145.90	$145.90
7 purchase totals =	$1,314.03		$1,417.9836	$1,417.98	$1,417.95	$1,418.00