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	$37.51	4.842%	$39.3262	$39.33	$39.35	$39.30
Purchase #2	$151.95	6.403%	$161.6794	$161.68	$161.70	$161.70
Purchase #3	$243.59	10.582%	$269.3667	$269.37	$269.35	$269.40
Purchase #4	$206.43	7.870%	$222.676	$222.68	$222.70	$222.70
Purchase #5	$81.79	9.656%	$89.6876	$89.69	$89.70	$89.70
Purchase #6	$38.30	5.342%	$40.346	$40.35	$40.35	$40.30
Purchase #7	$32.59	5.333%	$34.328	$34.33	$34.35	$34.30
7 purchase totals =	$792.16		$857.4099	$857.43	$857.50	$857.40