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	$157.42	5.451%	$166.001	$166.00	$166.00	$166.00
Purchase #2	$109.66	11.158%	$121.8959	$121.90	$121.90	$121.90
Purchase #3	$53.50	6.496%	$56.9754	$56.98	$57.00	$57.00
Purchase #4	$81.31	9.473%	$89.0125	$89.01	$89.00	$89.00
Purchase #5	$124.78	7.467%	$134.0973	$134.10	$134.10	$134.10
Purchase #6	$37.78	13.535%	$42.8935	$42.89	$42.90	$42.90
Purchase #7	$49.56	9.314%	$54.176	$54.18	$54.20	$54.20
7 purchase totals =	$614.01		$665.0516	$665.06	$665.10	$665.10