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	$70.91	8.331%	$76.8175	$76.82	$76.80	$76.80
Purchase #2	$81.53	10.187%	$89.8355	$89.84	$89.85	$89.80
Purchase #3	$35.68	4.235%	$37.191	$37.19	$37.20	$37.20
Purchase #4	$193.70	9.789%	$212.6613	$212.66	$212.65	$212.70
Purchase #5	$115.31	11.462%	$128.5268	$128.53	$128.55	$128.50
Purchase #6	$35.31	9.418%	$38.6355	$38.64	$38.65	$38.60
Purchase #7	$70.80	10.401%	$78.1639	$78.16	$78.15	$78.20
7 purchase totals =	$603.24		$661.8315	$661.84	$661.85	$661.80