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	$232.90	3.235%	$240.4343	$240.43	$240.45	$240.40
Purchase #2	$127.57	11.222%	$141.8859	$141.89	$141.90	$141.90
Purchase #3	$226.56	8.529%	$245.8833	$245.88	$245.90	$245.90
Purchase #4	$100.82	4.771%	$105.6301	$105.63	$105.65	$105.60
Purchase #5	$152.63	9.367%	$166.9269	$166.93	$166.95	$166.90
Purchase #6	$208.31	13.854%	$237.1693	$237.17	$237.15	$237.20
Purchase #7	$89.95	11.234%	$100.055	$100.06	$100.05	$100.10
7 purchase totals =	$1,138.74		$1,237.9848	$1,237.99	$1,238.05	$1,238.00