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	$134.85	6.798%	$144.0171	$144.02	$144.00	$144.00
Purchase #2	$20.82	3.614%	$21.5724	$21.57	$21.55	$21.60
Purchase #3	$206.60	11.269%	$229.8818	$229.88	$229.90	$229.90
Purchase #4	$130.55	11.649%	$145.7578	$145.76	$145.75	$145.80
Purchase #5	$202.71	7.588%	$218.0916	$218.09	$218.10	$218.10
Purchase #6	$248.56	12.272%	$279.0633	$279.06	$279.05	$279.10
Purchase #7	$80.47	6.380%	$85.604	$85.60	$85.60	$85.60
7 purchase totals =	$1,024.56		$1,123.9880	$1,123.98	$1,123.95	$1,124.10