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	$189.55	11.248%	$210.8706	$210.87	$210.85	$210.90
Purchase #2	$168.65	4.287%	$175.88	$175.88	$175.90	$175.90
Purchase #3	$68.65	12.872%	$77.4866	$77.49	$77.50	$77.50
Purchase #4	$33.43	9.354%	$36.557	$36.56	$36.55	$36.60
Purchase #5	$236.69	10.331%	$261.1424	$261.14	$261.15	$261.10
Purchase #6	$86.85	4.253%	$90.5437	$90.54	$90.55	$90.50
Purchase #7	$59.93	3.847%	$62.2355	$62.24	$62.25	$62.20
7 purchase totals =	$843.75		$914.7158	$914.72	$914.75	$914.70