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	$29.71	9.109%	$32.4163	$32.42	$32.40	$32.40
Purchase #2	$73.73	10.486%	$81.4613	$81.46	$81.45	$81.50
Purchase #3	$162.43	4.376%	$169.5379	$169.54	$169.55	$169.50
Purchase #4	$179.81	6.614%	$191.7026	$191.70	$191.70	$191.70
Purchase #5	$105.47	5.416%	$111.1823	$111.18	$111.20	$111.20
Purchase #6	$49.62	7.763%	$53.472	$53.47	$53.45	$53.50
Purchase #7	$178.55	10.313%	$196.9639	$196.96	$196.95	$197.00
7 purchase totals =	$779.32		$836.7363	$836.73	$836.70	$836.80