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	$97.91	6.443%	$104.2183	$104.22	$104.20	$104.20
Purchase #2	$198.64	13.545%	$225.5458	$225.55	$225.55	$225.50
Purchase #3	$163.81	9.573%	$179.4915	$179.49	$179.50	$179.50
Purchase #4	$59.86	7.611%	$64.4159	$64.42	$64.40	$64.40
Purchase #5	$92.73	6.741%	$98.9809	$98.98	$99.00	$99.00
Purchase #6	$75.48	6.500%	$80.3862	$80.39	$80.40	$80.40
Purchase #7	$55.69	3.264%	$57.5077	$57.51	$57.50	$57.50
7 purchase totals =	$744.12		$810.5463	$810.56	$810.55	$810.50